refactor(time): one timestamp formatter honouring the clock/date settings (#139)

Audit of every rendered time found five families of ad-hoc formatting:
the shared Time component + copies of its today/yesterday branch
(forwarded header, thread summary, read receipts, device tile, moderation
alerts, edit history), locale-default toLocale*String calls that ignored
the user's 12/24 h and date-format settings (scheduled tray, reminders,
schedule preview, notification snooze, bookmarks, threads list, search
cache line, room insights, media gallery), a hard-coded en-US date in the
activity log, and three relative-age variants.

utils/formatTimestamp.ts now holds the rules — today → time; yesterday /
tomorrow → day word + time; last 6 days → weekday + time; older → date +
time in dateFormatString — plus autoDate / time / date / dateTime styles,
formatDayDivider (full weekday), formatShortAge (room list) and
formatRelativeAge (list rows). useTimestampFormatter binds them to the
settings. 11 unit tests with an injected 'now'.

Visible changes are limited to consistency: 12 h times keep the existing
zero-padded hh:mm A; the a11y label and Created-by line use the user's
date format instead of a fixed long month.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/event-readers/EventReaders.tsx

@@ -24,32 +24,19 @@ import { useSpaceOptionally } from '../../hooks/useSpace';
 import { getMouseEventCords } from '../../utils/dom';
 import { useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
-import { today, yesterday, timeHourMinute, timeMon, timeDay, timeYear } from '../../utils/time';
+import { TimestampPrefs, formatTimestamp } from '../../utils/formatTimestamp';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
 
-function formatReadTs(ts: number, hour24Clock: boolean): string {
+const formatReadTs = (ts: number, prefs: TimestampPrefs): string => formatTimestamp(ts, prefs);
-  const timeStr = timeHourMinute(ts, hour24Clock);
-  if (today(ts)) return `Today at ${timeStr}`;
-  if (yesterday(ts)) return `Yesterday at ${timeStr}`;
-  const sameYear = timeYear(ts) === timeYear(Date.now());
-  return sameYear
-    ? `${timeMon(ts)} ${timeDay(ts)} at ${timeStr}`
-    : `${timeMon(ts)} ${timeDay(ts)} ${timeYear(ts)} at ${timeStr}`;
-}
 
 type EventReaderItemProps = {
   room: Room;
   readerId: string;
-  hour24Clock: boolean;
+  prefs: TimestampPrefs;
   lotusTerminal: boolean;
   onSelect: React.MouseEventHandler<HTMLButtonElement>;
 };
-function EventReaderItem({
+function EventReaderItem({ room, readerId, prefs, lotusTerminal, onSelect }: EventReaderItemProps) {
-  room,
-  readerId,
-  hour24Clock,
-  lotusTerminal,
-  onSelect,
-}: EventReaderItemProps) {
   const { name, avatarUrl } = useMemberAvatar(room, readerId, 100, 100);
   const receiptTs = room.getReadReceiptForUserId(readerId)?.data.ts;
 
@@ -86,7 +73,7 @@ function EventReaderItem({
                 : undefined
             }
           >
-            {formatReadTs(receiptTs, hour24Clock)}
+            {formatReadTs(receiptTs, prefs)}
           </Text>
         )}
       </Box>
@@ -106,7 +93,7 @@ export const EventReaders = as<'div', EventReadersProps>(
     const latestEventReaders = useRoomEventReaders(room, eventId).filter((id) => id !== myUserId);
     const openProfile = useOpenUserRoomProfile();
     const space = useSpaceOptionally();
-    const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+    const { prefs } = useTimestampFormatter();
     const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
 
     return (
@@ -157,7 +144,7 @@ export const EventReaders = as<'div', EventReadersProps>(
                   key={readerId}
                   room={room}
                   readerId={readerId}
-                  hour24Clock={hour24Clock}
+                  prefs={prefs}
                   lotusTerminal={lotusTerminal}
                   onSelect={(event) => {
                     openProfile(

src/app/components/message/ForwardedHeader.tsx

@@ -6,7 +6,7 @@ import * as css from './Reply.css';
 import { ForwardedMeta } from '../../features/room/message/forwardContent';
 import { getMemberDisplayName } from '../../utils/room';
 import { getMxIdLocalPart } from '../../utils/matrix';
-import { timeDayMonYear, timeHourMinute, today, yesterday } from '../../utils/time';
+import { formatTimestamp } from '../../utils/formatTimestamp';
 
 type ForwardedHeaderProps = {
   mx: MatrixClient;
@@ -32,11 +32,7 @@ export const ForwardedHeader = as<'div', ForwardedHeaderProps>(
       getMxIdLocalPart(meta.sender) ??
       meta.sender;
     const ts = meta.origin_server_ts;
-    const when = today(ts)
+    const when = formatTimestamp(ts, { hour24Clock, dateFormatString });
-      ? timeHourMinute(ts, hour24Clock)
-      : yesterday(ts)
-        ? `Yesterday ${timeHourMinute(ts, hour24Clock)}`
-        : `${timeDayMonYear(ts, dateFormatString)} ${timeHourMinute(ts, hour24Clock)}`;
     const canJump = !!sourceRoom && !!onJump;
 
     return (

src/app/components/message/Time.tsx

@@ -1,6 +1,6 @@
 import React, { ComponentProps } from 'react';
 import { Text, as } from 'folds';
-import { timeDayMonYear, timeHourMinute, today, yesterday } from '../../utils/time';
+import { formatTimestamp } from '../../utils/formatTimestamp';
 
 export type TimeProps = {
   compact?: boolean;
@@ -12,8 +12,8 @@ export type TimeProps = {
 /**
  * Renders a formatted timestamp, supporting compact and full display modes.
  *
- * Displays the time in hour:minute format if the message is from today, yesterday, or if `compact` is true.
+ * `compact` always shows the clock time; otherwise the shared `formatTimestamp`
- * For older messages, it shows the date and time.
+ * rules apply (today → time, yesterday/this week → day word + time, else date + time).
  *
  * @param {number} ts - The timestamp to display.
  * @param {boolean} [compact=false] - If true, always show only the time.
@@ -23,18 +23,7 @@ export type TimeProps = {
  */
 export const Time = as<'span', TimeProps & ComponentProps<typeof Text>>(
   ({ compact, hour24Clock, dateFormatString, ts, ...props }, ref) => {
-    const formattedTime = timeHourMinute(ts, hour24Clock);
+    const time = formatTimestamp(ts, { hour24Clock, dateFormatString }, compact ? 'time' : 'auto');
-
-    let time = '';
-    if (compact) {
-      time = formattedTime;
-    } else if (today(ts)) {
-      time = formattedTime;
-    } else if (yesterday(ts)) {
-      time = `Yesterday ${formattedTime}`;
-    } else {
-      time = `${timeDayMonYear(ts, dateFormatString)} ${formattedTime}`;
-    }
 
     return (
       <Text as="time" style={{ flexShrink: 0 }} size="T200" priority="300" {...props} ref={ref}>

src/app/components/room-intro/RoomIntro.tsx

@@ -19,15 +19,13 @@ import { getMemberDisplayName, getStateEvent } from '../../utils/room';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { getMxIdLocalPart, mxcUrlToHttp } from '../../utils/matrix';
 import { AsyncStatus, useAsyncCallback } from '../../hooks/useAsyncCallback';
-import { timeDayMonthYear, timeHourMinute } from '../../utils/time';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
 import { useRoomNavigate } from '../../hooks/useRoomNavigate';
 import { RoomAvatar } from '../room-avatar';
 import { nameInitials } from '../../utils/common';
 import { useRoomAvatar, useLocalRoomName, useRoomTopic } from '../../hooks/useRoomMeta';
 import { mDirectAtom } from '../../state/mDirectList';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
-import { useSetting } from '../../state/hooks/settings';
-import { settingsAtom } from '../../state/settings';
 import { InviteUserPrompt } from '../invite-user-prompt';
 import { RoomTopicViewer } from '../room-topic-viewer';
 import { stopPropagation } from '../../utils/keyboard';
@@ -68,7 +66,7 @@ export const RoomIntro = as<'div', RoomIntroProps>(({ room, ...props }, ref) =>
     useCallback(async (roomId: string) => mx.joinRoom(roomId), [mx]),
   );
 
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
 
   return (
     <Box direction="Column" grow="Yes" gap="500" {...props} ref={ref}>
@@ -135,7 +133,7 @@ export const RoomIntro = as<'div', RoomIntroProps>(({ room, ...props }, ref) =>
             <Text size="T200" priority="300">
               {'Created by '}
               <b>@{creatorName}</b>
-              {` on ${timeDayMonthYear(ts)} ${timeHourMinute(ts, hour24Clock)}`}
+              {` on ${format(ts, 'dateTime')}`}
             </Text>
           )}
         </Box>

src/app/components/user-profile/UserModeration.tsx

@@ -6,9 +6,7 @@ import { SettingTile } from '../setting-tile';
 import { AsyncStatus, useAsyncCallback } from '../../hooks/useAsyncCallback';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { BreakWord } from '../../styles/Text.css';
-import { useSetting } from '../../state/hooks/settings';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
-import { settingsAtom } from '../../state/settings';
-import { timeDayMonYear, timeHourMinute } from '../../utils/time';
 
 type UserKickAlertProps = {
   reason?: string;
@@ -16,11 +14,8 @@ type UserKickAlertProps = {
   ts?: number;
 };
 export function UserKickAlert({ reason, kickedBy, ts }: UserKickAlertProps) {
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
-  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
+  const when = ts ? format(ts) : undefined;
-
-  const time = ts ? timeHourMinute(ts, hour24Clock) : undefined;
-  const date = ts ? timeDayMonYear(ts, dateFormatString) : undefined;
 
   return (
     <CutoutCard style={{ padding: config.space.S200 }} variant="Critical">
@@ -28,11 +23,7 @@ export function UserKickAlert({ reason, kickedBy, ts }: UserKickAlertProps) {
         <Box direction="Column" gap="200">
           <Box gap="200" justifyContent="SpaceBetween">
             <Text size="L400">Kicked User</Text>
-            {time && date && (
+            {when && <Text size="T200">{when}</Text>}
-              <Text size="T200">
-                {date} {time}
-              </Text>
-            )}
           </Box>
           <Box direction="Column">
             {kickedBy && (
@@ -66,11 +57,8 @@ type UserBanAlertProps = {
 export function UserBanAlert({ userId, reason, canUnban, bannedBy, ts }: UserBanAlertProps) {
   const mx = useMatrixClient();
   const room = useRoom();
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
-  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
+  const when = ts ? format(ts) : undefined;
-
-  const time = ts ? timeHourMinute(ts, hour24Clock) : undefined;
-  const date = ts ? timeDayMonYear(ts, dateFormatString) : undefined;
 
   const [unbanState, unban] = useAsyncCallback<undefined, Error, []>(
     useCallback(async () => {
@@ -86,11 +74,7 @@ export function UserBanAlert({ userId, reason, canUnban, bannedBy, ts }: UserBan
         <Box direction="Column" gap="200">
           <Box gap="200" justifyContent="SpaceBetween">
             <Text size="L400">Banned User</Text>
-            {time && date && (
+            {when && <Text size="T200">{when}</Text>}
-              <Text size="T200">
-                {date} {time}
-              </Text>
-            )}
           </Box>
           <Box direction="Column">
             {bannedBy && (
@@ -141,11 +125,8 @@ type UserInviteAlertProps = {
 export function UserInviteAlert({ userId, reason, canKick, invitedBy, ts }: UserInviteAlertProps) {
   const mx = useMatrixClient();
   const room = useRoom();
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
-  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
+  const when = ts ? format(ts) : undefined;
-
-  const time = ts ? timeHourMinute(ts, hour24Clock) : undefined;
-  const date = ts ? timeDayMonYear(ts, dateFormatString) : undefined;
 
   const [kickState, kick] = useAsyncCallback<undefined, Error, []>(
     useCallback(async () => {
@@ -161,11 +142,7 @@ export function UserInviteAlert({ userId, reason, canKick, invitedBy, ts }: User
         <Box direction="Column" gap="200">
           <Box gap="200" justifyContent="SpaceBetween">
             <Text size="L400">Invited User</Text>
-            {time && date && (
+            {when && <Text size="T200">{when}</Text>}
-              <Text size="T200">
-                {date} {time}
-              </Text>
-            )}
           </Box>
           <Box direction="Column">
             {invitedBy && (

src/app/features/bookmarks/BookmarksPanel.tsx

@@ -35,19 +35,8 @@ import { nameInitials } from '../../utils/common';
 import { ContainerColor } from '../../styles/ContainerColor.css';
 import { stopPropagation } from '../../utils/keyboard';
 import * as css from './BookmarksPanel.css';
-
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
-function formatTimeAgo(ts: number): string {
+import { formatRelativeAge } from '../../utils/formatTimestamp';
-  const diff = Date.now() - ts;
-  const minutes = Math.floor(diff / 60_000);
-  if (minutes < 1) return 'just now';
-  if (minutes < 60) return `${minutes}m ago`;
-  const hours = Math.floor(minutes / 60);
-  if (hours < 24) return `${hours}h ago`;
-  const days = Math.floor(hours / 24);
-  if (days === 1) return 'yesterday';
-  if (days < 7) return `${days}d ago`;
-  return new Date(ts).toLocaleDateString();
-}
 
 // Remember the last-chosen sort across panel opens (the panel unmounts on close).
 // getOnInit reads localStorage synchronously at init so the persisted sort is
@@ -110,7 +99,8 @@ function BookmarkItem({ bookmark, onJump, onRemove, preview, senderName }: Bookm
     : undefined;
   // Prefer a live-resolved author name, then the stored snapshot.
   const author = senderName ?? bookmark.senderName;
-  const timeAgo = formatTimeAgo(bookmark.savedAt);
+  const { prefs } = useTimestampFormatter();
+  const timeAgo = formatRelativeAge(bookmark.savedAt, prefs);
 
   return (
     <Box

src/app/features/message-search/MessageSearch.tsx

@@ -52,6 +52,7 @@ import { SearchResultGroup } from './SearchResultGroup';
 import { SearchInput } from './SearchInput';
 import { SearchFilters } from './SearchFilters';
 import { VirtualTile } from '../../components/virtualizer';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
 
 const useSearchPathSearchParams = (searchParams: URLSearchParams): _SearchPathSearchParams =>
   useMemo(
@@ -74,6 +75,7 @@ type EncryptedRoomCachePanelProps = {
 };
 function EncryptedRoomCachePanel({ roomIds, onLoaded }: EncryptedRoomCachePanelProps) {
   const mx = useMatrixClient();
+  const { format } = useTimestampFormatter();
   const [loadingRooms, setLoadingRooms] = useState<Set<string>>(new Set());
 
   const encryptedRooms = useMemo(
@@ -140,7 +142,7 @@ function EncryptedRoomCachePanel({ roomIds, onLoaded }: EncryptedRoomCachePanelP
               </Text>
               <Text size="T200" priority="300">
                 {msgEvents.length > 0
-                  ? `${msgEvents.length} messages cached · oldest: ${new Date(oldest!.getTs()).toLocaleDateString()}`
+                  ? `${msgEvents.length} messages cached · oldest: ${format(oldest!.getTs(), 'date')}`
                   : 'No messages cached yet'}
               </Text>
             </Box>

src/app/features/room-nav/RoomNavItem.tsx

@@ -37,9 +37,6 @@ import { useFocusWithin, useHover } from 'react-aria';
 import FocusTrap from 'focus-trap-react';
 import { useAtom, useAtomValue, useSetAtom } from 'jotai';
 import { selectAtom } from 'jotai/utils';
-import dayjs from 'dayjs';
-import isToday from 'dayjs/plugin/isToday';
-import isYesterday from 'dayjs/plugin/isYesterday';
 import { NavItem, NavItemContent, NavItemOptions, NavLink } from '../../components/nav';
 import { UnreadBadge, UnreadBadgeCenter } from '../../components/unread-badge';
 import { RoomAvatar, RoomIcon } from '../../components/room-avatar';
@@ -97,29 +94,11 @@ import { MessageEvent, StateEvent } from '../../../types/matrix/room';
 import { webRTCSupported } from '../../utils/rtc';
 import { useRoomLatestRenderedEvent } from '../../hooks/useRoomLatestRenderedEvent';
 import { EmojiBoard } from '../../components/emoji-board';
-
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
-dayjs.extend(isToday);
+import { formatShortAge } from '../../utils/formatTimestamp';
-dayjs.extend(isYesterday);
 
 const PREVIEW_MAX_CHARS = 48;
 
-function formatDmTimestamp(ts: number): string {
-  const d = dayjs(ts);
-  const now = dayjs();
-  const diffMinutes = now.diff(d, 'minute');
-  if (diffMinutes < 60) {
-    return `${diffMinutes < 1 ? 0 : diffMinutes}m`;
-  }
-  const diffHours = now.diff(d, 'hour');
-  if (diffHours < 24) {
-    return `${diffHours}h`;
-  }
-  if (d.isYesterday()) {
-    return 'Yesterday';
-  }
-  return d.format('D MMM');
-}
-
 type RenameRoomDialogProps = {
   room: Room;
   onClose: () => void;
@@ -646,6 +625,7 @@ function RoomNavItem_({
 
   const roomName = useLocalRoomName(room);
   const hasLocalName = useHasLocalRoomName(room.roomId);
+  const { prefs } = useTimestampFormatter();
 
   // Whether this room has an unsent message draft. selectAtom maps to a boolean
   // so the row only re-renders when that flips (the draft atom itself is written
@@ -677,7 +657,7 @@ function RoomNavItem_({
     }
     if (!body) return null;
     const preview = body.length > PREVIEW_MAX_CHARS ? `${body.slice(0, PREVIEW_MAX_CHARS)}…` : body;
-    return { preview, time: formatDmTimestamp(ts) };
+    return { preview, time: formatShortAge(ts, prefs) };
   })();
 
   const handleContextMenu: MouseEventHandler<HTMLElement> = (evt) => {

src/app/features/room-settings/RoomActivityLog.tsx

@@ -9,6 +9,8 @@ import {
   createDetachedTimelineSet,
   createTypesFilter,
 } from '../../utils/detachedTimeline';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
+import { formatRelativeAge } from '../../utils/formatTimestamp';
 
 // ── Types ─────────────────────────────────────────────────────────────────────
 
@@ -27,20 +29,6 @@ type StateEventType = (typeof STATE_EVENT_TYPES)[number];
 
 // ── Timestamp formatting ──────────────────────────────────────────────────────
 
-function formatRelativeTs(ts: number): string {
-  const diff = Date.now() - ts;
-  if (diff < 60000) return 'just now';
-  if (diff < 3600000) return `${Math.floor(diff / 60000)}m ago`;
-  if (diff < 86400000) return `${Math.floor(diff / 3600000)}h ago`;
-  const d = new Date(ts);
-  const sameYear = d.getFullYear() === new Date().getFullYear();
-  return d.toLocaleDateString('en-US', {
-    month: 'short',
-    day: 'numeric',
-    ...(sameYear ? {} : { year: 'numeric' }),
-  });
-}
-
 // ── Event description ─────────────────────────────────────────────────────────
 
 function getDisplayName(mx: ReturnType<typeof useMatrixClient>, userId: string): string {
@@ -296,6 +284,7 @@ type LogEntryProps = {
 };
 
 function LogEntry({ ev, desc }: LogEntryProps) {
+  const { prefs } = useTimestampFormatter();
   return (
     <Box
       alignItems="Center"
@@ -326,7 +315,7 @@ function LogEntry({ ev, desc }: LogEntryProps) {
           {desc.text}
         </Text>
         <Text size="T200" priority="300">
-          {formatRelativeTs(ev.getTs())}
+          {formatRelativeAge(ev.getTs(), prefs)}
         </Text>
       </Box>
     </Box>

src/app/features/room-settings/RoomInsights.tsx

@@ -9,21 +9,10 @@ import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { getMemberAvatarMxc, getMemberName } from '../../utils/room';
 import { mxcUrlToHttp } from '../../utils/matrix';
 import { UserAvatar } from '../../components/user-avatar';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
 
 // ── Helpers ───────────────────────────────────────────────────────────────────
 
-function formatDate(ts: number): string {
-  return new Date(ts).toLocaleDateString(undefined, {
-    month: 'short',
-    day: 'numeric',
-    year: 'numeric',
-  });
-}
-
-function formatUpdatedAt(ts: number): string {
-  return new Date(ts).toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' });
-}
-
 // Throttle window for re-computing stats on new timeline events - avoids
 // re-running every heatmap/list computation on every single incoming message
 // during a burst.
@@ -74,6 +63,7 @@ type RoomInsightsProps = {
 };
 
 export function RoomInsights({ requestClose }: RoomInsightsProps) {
+  const { format } = useTimestampFormatter();
   const mx = useMatrixClient();
   const room = useRoom();
   const useAuthentication = useMediaAuthentication();
@@ -234,11 +224,11 @@ export function RoomInsights({ requestClose }: RoomInsightsProps) {
                   </Text>
                   {stats.oldestTs !== null && stats.newestTs !== null && (
                     <Text size="T200" priority="300">
-                      from {formatDate(stats.oldestTs)} to {formatDate(stats.newestTs)}
+                      from {format(stats.oldestTs, 'date')} to {format(stats.newestTs, 'date')}
                     </Text>
                   )}
                   <Text size="T200" priority="300">
-                    Last updated {formatUpdatedAt(lastUpdated)}
+                    Last updated {format(lastUpdated, 'time')}
                   </Text>
                 </Box>
                 <Box shrink="No">

src/app/features/room/MediaGallery.tsx

@@ -35,6 +35,8 @@ import { useRoomMediaTimeline } from '../../hooks/useRoomMediaTimeline';
 import { ContainerColor } from '../../styles/ContainerColor.css';
 import { stopPropagation } from '../../utils/keyboard';
 import * as css from './MediaGallery.css';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
+import { formatRelativeAge } from '../../utils/formatTimestamp';
 
 type GalleryTab = 'image' | 'video' | 'file' | 'audio';
 
@@ -117,18 +119,6 @@ function useDecryptedMediaUrl(
 
 // ── Helpers ───────────────────────────────────────────────────────────────────
 
-function formatRelativeDate(ts: number): string {
-  const diff = Date.now() - ts;
-  const mins = Math.floor(diff / 60000);
-  if (mins < 2) return 'Just now';
-  if (mins < 60) return `${mins}m ago`;
-  const hrs = Math.floor(diff / 3600000);
-  if (hrs < 24) return `${hrs}h ago`;
-  const days = Math.floor(diff / 86400000);
-  if (days < 7) return `${days}d ago`;
-  return new Date(ts).toLocaleDateString(undefined, { month: 'short', day: 'numeric' });
-}
-
 function formatBytes(bytes: number): string {
   if (bytes < 1024) return `${bytes} B`;
   if (bytes < 1048576) return `${(bytes / 1024).toFixed(1)} KB`;
@@ -323,6 +313,7 @@ export function Lightbox({
   onJump: (eventId: string) => void;
 }) {
   const [index, setIndex] = useState(initialIndex);
+  const { format } = useTimestampFormatter();
 
   const item = items[index];
   const isImage = item?.msgtype === MsgType.Image;
@@ -366,11 +357,7 @@ export function Lightbox({
 
   if (!item) return null;
 
-  const dateStr = new Date(item.ts).toLocaleDateString(undefined, {
+  const dateStr = format(item.ts, 'date');
-    month: 'short',
-    day: 'numeric',
-    year: 'numeric',
-  });
 
   return (
     <Overlay open backdrop={<OverlayBackdrop />}>
@@ -614,7 +601,8 @@ function GalleryTile({
     mimeType,
     nearViewport,
   );
-  const relDate = formatRelativeDate(ts);
+  const { prefs } = useTimestampFormatter();
+  const relDate = formatRelativeAge(ts, prefs);
 
   return (
     <div className={css.GalleryTileWrap}>
@@ -724,6 +712,7 @@ type MediaGalleryProps = {
 };
 
 export function MediaGallery({ room, onClose }: MediaGalleryProps) {
+  const { prefs } = useTimestampFormatter();
   const mx = useMatrixClient();
   const useAuthentication = useMediaAuthentication();
   const { navigateRoom } = useRoomNavigate();
@@ -1040,7 +1029,7 @@ export function MediaGallery({ room, onClose }: MediaGalleryProps) {
                       if (!url) return null;
                       const body: string = c.body || 'Voice message';
                       const sender = getSenderName(room, mEvent.getSender() ?? '');
-                      const relDate = formatRelativeDate(mEvent.getTs());
+                      const relDate = formatRelativeAge(mEvent.getTs(), prefs);
                       // Sanitize the mimetype the way MAudio does (e.g. application/ogg →
                       // audio/ogg) so the decrypted blob actually plays.
                       const mimeType = getBlobSafeMimeType(c.info?.mimetype ?? 'audio/ogg');

src/app/features/room/RoomTimeline.tsx

@@ -105,7 +105,8 @@ import { markAsRead } from '../../utils/notifications';
 import { useDebounce } from '../../hooks/useDebounce';
 import { getResizeObserverEntry, useResizeObserver } from '../../hooks/useResizeObserver';
 import * as css from './RoomTimeline.css';
-import { inSameDay, minuteDifference, timeDayMonthYear, today, yesterday } from '../../utils/time';
+import { inSameDay, minuteDifference } from '../../utils/time';
+import { formatDayDivider } from '../../utils/formatTimestamp';
 import { createMentionElement, isEmptyEditor, moveCursor } from '../../components/editor';
 import { roomIdToReplyDraftAtomFamily } from '../../state/room/roomInputDrafts';
 import { roomIdToActiveThreadIdAtomFamily } from '../../state/room/thread';
@@ -2282,11 +2283,7 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
           <TimelineDivider variant="Surface">
             <Badge as="span" size="500" variant="Secondary" fill="None" radii="300">
               <Text size="L400">
-                {(() => {
+                {formatDayDivider(mEvent.getTs(), { hour24Clock, dateFormatString })}
-                  if (today(mEvent.getTs())) return 'Today';
-                  if (yesterday(mEvent.getTs())) return 'Yesterday';
-                  return timeDayMonthYear(mEvent.getTs());
-                })()}
               </Text>
             </Badge>
           </TimelineDivider>

src/app/features/room/ScheduleMessageModal.tsx

@@ -17,6 +17,7 @@ import {
   config,
 } from 'folds';
 import { IContent } from 'matrix-js-sdk';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { stopPropagation } from '../../utils/keyboard';
 import { scheduleMessage } from '../../utils/scheduledMessages';
@@ -101,6 +102,7 @@ export function ScheduleMessageModal({
   };
 
   // When editing, seed the pickers from the existing send-time; else default to +1h.
+  const { prefs } = useTimestampFormatter();
   const def = initialSendAt ? new Date(initialSendAt) : defaultDate();
   const [dateValue, setDateValue] = useState<string>(() => toLocalDate(def));
   const [timeValue, setTimeValue] = useState<string>(() => toLocalTime(def));
@@ -124,10 +126,10 @@ export function ScheduleMessageModal({
       return;
     }
     setPreview({
-      label: formatFriendlyDateTime(sendAt.getTime()),
+      label: formatFriendlyDateTime(sendAt.getTime(), prefs),
       relative: formatRelativeTime(diffMs),
     });
-  }, [getSendAt]);
+  }, [getSendAt, prefs]);
 
   useEffect(() => {
     updatePreview();

src/app/features/room/ScheduledMessagesTray.tsx

@@ -6,32 +6,17 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { scheduledMessagesAtom, ScheduledMessage } from '../../state/scheduledMessages';
 import { cancelScheduledMessage, sendScheduledMessageNow } from '../../utils/scheduledMessages';
 import { ScheduleMessageModal } from './ScheduleMessageModal';
+import { useTimestampFormatter } from '../../hooks/useTimestampFormatter';
+import { formatFriendlyDateTime } from '../../utils/datetimeInput';
 
 interface ScheduledMessagesTrayProps {
   roomId: string;
 }
 
-function formatSendAt(sendAt: number): string {
-  const date = new Date(sendAt);
-  const now = new Date();
-  const isToday =
-    date.getFullYear() === now.getFullYear() &&
-    date.getMonth() === now.getMonth() &&
-    date.getDate() === now.getDate();
-  const tomorrow = new Date(now);
-  tomorrow.setDate(tomorrow.getDate() + 1);
-  const isTomorrow =
-    date.getFullYear() === tomorrow.getFullYear() &&
-    date.getMonth() === tomorrow.getMonth() &&
-    date.getDate() === tomorrow.getDate();
-  const timeStr = date.toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
-  if (isToday) return `Today ${timeStr}`;
-  if (isTomorrow) return `Tomorrow ${timeStr}`;
-  return `${date.toLocaleDateString()} ${timeStr}`;
-}
-
 export function ScheduledMessagesTray({ roomId }: ScheduledMessagesTrayProps) {
   const mx = useMatrixClient();
+  const { prefs } = useTimestampFormatter();
+  const formatSendAt = (sendAt: number) => formatFriendlyDateTime(sendAt, prefs);
   const [scheduledMessages, setScheduledMessages] = useAtom(scheduledMessagesAtom);
   const [expanded, setExpanded] = useState(false);
   const [cancelling, setCancelling] = useState<Set<string>>(new Set());

src/app/features/room/jump-to-time/JumpToTime.tsx

@@ -27,7 +27,8 @@ import { useAlive } from '../../../hooks/useAlive';
 import { useStateEvent } from '../../../hooks/useStateEvent';
 import { useRoom } from '../../../hooks/useRoom';
 import { StateEvent } from '../../../../types/matrix/room';
-import { getToday, getYesterday, timeDayMonthYear, timeHourMinute } from '../../../utils/time';
+import { getToday, getYesterday } from '../../../utils/time';
+import { formatDate, formatTime } from '../../../utils/formatTimestamp';
 import { DatePicker, TimePicker } from '../../../components/time-date';
 import { useSetting } from '../../../state/hooks/settings';
 import { settingsAtom } from '../../../state/settings';
@@ -50,6 +51,7 @@ export function JumpToTime({ onCancel, onSubmit }: JumpToTimeProps) {
   const [ts, setTs] = useState(() => Date.now());
 
   const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
 
   const [timePickerCords, setTimePickerCords] = useState<RectCords>();
   const [datePickerCords, setDatePickerCords] = useState<RectCords>();
@@ -131,7 +133,7 @@ export function JumpToTime({ onCancel, onSubmit }: JumpToTimeProps) {
                       after={<Icon size="50" src={Icons.ChevronBottom} />}
                       onClick={handleTimePicker}
                     >
-                      <Text size="B300">{timeHourMinute(ts, hour24Clock)}</Text>
+                      <Text size="B300">{formatTime(ts, { hour24Clock })}</Text>
                     </Chip>
                     <PopOut
                       anchor={timePickerCords}
@@ -172,7 +174,7 @@ export function JumpToTime({ onCancel, onSubmit }: JumpToTimeProps) {
                       after={<Icon size="50" src={Icons.ChevronBottom} />}
                       onClick={handleDatePicker}
                     >
-                      <Text size="B300">{timeDayMonthYear(ts)}</Text>
+                      <Text size="B300">{formatDate(ts, { hour24Clock, dateFormatString })}</Text>
                     </Chip>
                     <PopOut
                       anchor={datePickerCords}

src/app/features/room/message/EditHistoryModal.tsx

@@ -27,7 +27,7 @@ import { useModalStyle } from '../../../hooks/useModalStyle';
 import { sanitizeCustomHtml } from '../../../utils/sanitize';
 import { LINKIFY_OPTS } from '../../../plugins/react-custom-html-parser';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
-import { timeDayMonYear, timeHourMinute } from '../../../utils/time';
+import { formatTimestamp } from '../../../utils/formatTimestamp';
 import { useSetting } from '../../../state/hooks/settings';
 import { settingsAtom } from '../../../state/settings';
 import { diffWords } from '../../../utils/textDiff';
@@ -229,11 +229,7 @@ export function EditHistoryModal({ room, mEvent, onClose }: EditHistoryModalProp
   const initialLoading = historyState.status === AsyncStatus.Loading && edits.length === 0;
   const loadingMore = historyState.status === AsyncStatus.Loading && edits.length > 0;
 
-  const formatTs = (ts: number): string => {
+  const formatTs = (ts: number): string => formatTimestamp(ts, { hour24Clock, dateFormatString });
-    const time = timeHourMinute(ts, hour24Clock);
-    const date = timeDayMonYear(ts, dateFormatString);
-    return `${date} at ${time}`;
-  };
 
   const originalContent = getOriginalContent(mEvent);
 

src/app/features/room/message/Message.tsx

@@ -1334,7 +1334,12 @@ export const Message = React.memo(
           })}
           role="article"
           aria-label={
-            collapse ? messageAriaLabel(senderDisplayName, mEvent.getTs(), hour24Clock) : undefined
+            collapse
+              ? messageAriaLabel(senderDisplayName, mEvent.getTs(), {
+                  hour24Clock,
+                  dateFormatString,
+                })
+              : undefined
           }
           tabIndex={0}
           space={messageSpacing}

src/app/features/room/message/RemindMeDialog.tsx

@@ -16,6 +16,8 @@ import {
   OverlayCenter,
   Text,
 } from 'folds';
+import { TimestampPrefs, formatTime } from '../../../utils/formatTimestamp';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
 import { stopPropagation } from '../../../utils/keyboard';
 import { useReminders } from '../../../hooks/useReminders';
 import { useModalStyle } from '../../../hooks/useModalStyle';
@@ -34,11 +36,11 @@ type RemindMeDialogProps = {
   onClose: () => void;
 };
 
-function getPresets(): Array<{ label: string; ms: number }> {
+function getPresets(prefs: TimestampPrefs): Array<{ label: string; ms: number }> {
   const tomorrow = new Date();
   tomorrow.setDate(tomorrow.getDate() + 1);
   tomorrow.setHours(9, 0, 0, 0);
-  const timeLabel = tomorrow.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+  const timeLabel = formatTime(tomorrow.getTime(), prefs);
   return [
     { label: 'In 20 minutes', ms: 20 * 60_000 },
     { label: 'In 1 hour', ms: 60 * 60_000 },
@@ -58,7 +60,8 @@ function defaultCustomDate(): Date {
 export function RemindMeDialog({ roomId, eventId, previewText, onClose }: RemindMeDialogProps) {
   const modalStyle = useModalStyle(320);
   const { addReminder, removeReminder, reminders } = useReminders();
-  const presets = useMemo(() => getPresets(), []);
+  const { prefs } = useTimestampFormatter();
+  const presets = useMemo(() => getPresets(prefs), [prefs]);
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [customOpen, setCustomOpen] = useState(false);
@@ -185,7 +188,7 @@ export function RemindMeDialog({ roomId, eventId, previewText, onClose }: Remind
                     <Box key={`${r.timestamp}-${idx}`} alignItems="Center" gap="200">
                       <Icon src={Icons.Clock} size="100" style={{ flexShrink: 0 }} />
                       <Text size="T200" style={{ flexGrow: 1, minWidth: 0 }} truncate>
-                        {formatFriendlyDateTime(r.timestamp)}
+                        {formatFriendlyDateTime(r.timestamp, prefs)}
                       </Text>
                       <IconButton
                         size="300"
@@ -193,7 +196,7 @@ export function RemindMeDialog({ roomId, eventId, previewText, onClose }: Remind
                         variant="SurfaceVariant"
                         fill="None"
                         onClick={() => handleCancelExisting(r.timestamp)}
-                        aria-label={`Cancel reminder for ${formatFriendlyDateTime(r.timestamp)}`}
+                        aria-label={`Cancel reminder for ${formatFriendlyDateTime(r.timestamp, prefs)}`}
                       >
                         <Icon src={Icons.Cross} size="100" />
                       </IconButton>

src/app/features/room/thread/ThreadSummary.tsx

@@ -3,9 +3,7 @@ import { Badge, Box, Chip, Icon, Icons, Text, config } from 'folds';
 import { MatrixEvent, Room } from 'matrix-js-sdk';
 import { MobileTouchTarget } from '../../../styles/mobile.css';
 import { useThreadSummary } from '../../../hooks/useThreadSummary';
-import { useSetting } from '../../../state/hooks/settings';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
-import { settingsAtom } from '../../../state/settings';
-import { timeDayMonthYear, timeHourMinute, today } from '../../../utils/time';
 import { ThreadNotificationMode } from '../../../utils/threadNotifications';
 
 type ThreadSummaryProps = {
@@ -15,17 +13,12 @@ type ThreadSummaryProps = {
 };
 export function ThreadSummary({ rootEvent, room, onOpen }: ThreadSummaryProps) {
   const { summary, unread, mode } = useThreadSummary(rootEvent, room);
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
 
   if (!summary || summary.count === 0) return null;
 
   const { count, latestTs } = summary;
-  const latestStr =
+  const latestStr = latestTs !== undefined ? format(latestTs) : undefined;
-    latestTs !== undefined
-      ? today(latestTs)
-        ? timeHourMinute(latestTs, hour24Clock)
-        : timeDayMonthYear(latestTs)
-      : undefined;
 
   return (
     <Box style={{ marginTop: config.space.S200 }}>

src/app/features/room/thread/ThreadTimeline.tsx

@@ -76,13 +76,8 @@ import { RoomMediaLightbox } from '../RoomMediaLightbox';
 import { Image } from '../../../components/media';
 import { ImageViewer } from '../../../components/image-viewer';
 import * as css from './ThreadTimeline.css';
-import {
+import { inSameDay, minuteDifference } from '../../../utils/time';
-  inSameDay,
+import { formatDayDivider } from '../../../utils/formatTimestamp';
-  minuteDifference,
-  timeDayMonthYear,
-  today,
-  yesterday,
-} from '../../../utils/time';
 import { createMentionElement, isEmptyEditor, moveCursor } from '../../../components/editor';
 import { useKeyDown } from '../../../hooks/useKeyDown';
 import { roomIdToReplyDraftAtomFamily } from '../../../state/room/roomInputDrafts';
@@ -910,11 +905,7 @@ export function ThreadTimeline({ room, thread, editor }: ThreadTimelineProps) {
             <Line style={{ flexGrow: 1 }} variant="Surface" size="300" />
             <Badge as="span" size="500" variant="Secondary" fill="None" radii="300">
               <Text size="L400">
-                {(() => {
+                {formatDayDivider(mEvent.getTs(), { hour24Clock, dateFormatString })}
-                  if (today(mEvent.getTs())) return 'Today';
-                  if (yesterday(mEvent.getTs())) return 'Yesterday';
-                  return timeDayMonthYear(mEvent.getTs());
-                })()}
               </Text>
             </Badge>
             <Line style={{ flexGrow: 1 }} variant="Surface" size="300" />

src/app/features/room/thread/ThreadsListPanel.tsx

@@ -27,6 +27,8 @@ import {
   isThreadSort,
 } from '../../../utils/threadList';
 import { useRoomThreads } from '../../../hooks/useRoomThreads';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
+import { formatRelativeAge } from '../../../utils/formatTimestamp';
 
 // Persisted across panel opens (the panel unmounts on close). getOnInit reads
 // localStorage synchronously so the chosen filter/sort apply on first render.
@@ -55,19 +57,6 @@ const SORT_OPTIONS: { value: ThreadSort; label: string }[] = [
 
 const MAX_PARTICIPANTS = 5;
 
-function formatTimeAgo(ts: number): string {
-  const diff = Date.now() - ts;
-  const minutes = Math.floor(diff / 60_000);
-  if (minutes < 1) return 'just now';
-  if (minutes < 60) return `${minutes}m ago`;
-  const hours = Math.floor(minutes / 60);
-  if (hours < 24) return `${hours}h ago`;
-  const days = Math.floor(hours / 24);
-  if (days === 1) return 'yesterday';
-  if (days < 7) return `${days}d ago`;
-  return new Date(ts).toLocaleDateString();
-}
-
 // Segmented button, mirroring the Bookmarks panel sort control for consistency.
 function SegButton({
   label,
@@ -115,6 +104,7 @@ type ThreadRowProps = {
   onOpen: (threadId: string) => void;
 };
 function ThreadRow({ room, thread, unread, highlight, participants, onOpen }: ThreadRowProps) {
+  const { prefs } = useTimestampFormatter();
   const rootEvent = thread.rootEvent;
   const rootSender = rootEvent?.getSender() ?? '';
   const { name: rootName, avatarUrl } = useMemberAvatar(room, rootSender);
@@ -126,7 +116,7 @@ function ThreadRow({ room, thread, unread, highlight, participants, onOpen }: Th
   const extra = participants.length - MAX_PARTICIPANTS;
   const replyLabel = `${count} ${count === 1 ? 'reply' : 'replies'}`;
   const ariaLabel = `Open thread by ${rootName}${unread > 0 ? ', unread' : ''}, ${replyLabel}${
-    typeof lastTs === 'number' ? `, last reply ${formatTimeAgo(lastTs)}` : ''
+    typeof lastTs === 'number' ? `, last reply ${formatRelativeAge(lastTs, prefs)}` : ''
   }`;
 
   return (
@@ -175,7 +165,7 @@ function ThreadRow({ room, thread, unread, highlight, participants, onOpen }: Th
         <Icon size="50" src={Icons.Thread} />
         <Text size="T200" priority="300" truncate style={{ flexGrow: 1 }}>
           {count} {count === 1 ? 'reply' : 'replies'}
-          {typeof lastTs === 'number' ? ` · ${formatTimeAgo(lastTs)}` : ''}
+          {typeof lastTs === 'number' ? ` · ${formatRelativeAge(lastTs, prefs)}` : ''}
         </Text>
         <Box shrink="No" alignItems="Center">
           {participants.slice(0, MAX_PARTICIPANTS).map((userId) => (

src/app/features/settings/devices/DeviceTile.tsx

@@ -20,15 +20,13 @@ import FocusTrap from 'focus-trap-react';
 import { IMyDevice, MatrixError } from 'matrix-js-sdk';
 import { SettingTile } from '../../../components/setting-tile';
 import { useMatrixClient } from '../../../hooks/useMatrixClient';
-import { timeDayMonYear, timeHourMinute, today, yesterday } from '../../../utils/time';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
 import { BreakWord } from '../../../styles/Text.css';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
 import { SequenceCard } from '../../../components/sequence-card';
 import { SequenceCardStyle } from '../styles.css';
 import { LogoutDialog } from '../../../components/LogoutDialog';
 import { stopPropagation } from '../../../utils/keyboard';
-import { useSetting } from '../../../state/hooks/settings';
-import { settingsAtom } from '../../../state/settings';
 
 export function DeviceTilePlaceholder() {
   return (
@@ -43,20 +41,14 @@ export function DeviceTilePlaceholder() {
 }
 
 function DeviceActiveTime({ ts }: { ts: number }) {
-  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const { format } = useTimestampFormatter();
-  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
 
   return (
     <Text className={BreakWord} size="T200">
       <Text size="Inherit" as="span" priority="300">
         {'Last activity: '}
       </Text>
-      <>
+      {format(ts)}
-        {today(ts) && 'Today'}
-        {yesterday(ts) && 'Yesterday'}
-        {!today(ts) && !yesterday(ts) && timeDayMonYear(ts, dateFormatString)}{' '}
-        {timeHourMinute(ts, hour24Clock)}
-      </>
     </Text>
   );
 }

src/app/features/settings/notifications/SystemNotification.tsx

@@ -2,6 +2,7 @@ import React, { useCallback, useEffect, useState } from 'react';
 import { Box, Text, Switch, Button, Chip, Icon, Icons, color, config, Spinner } from 'folds';
 import { IPusherRequest } from 'matrix-js-sdk';
 import { useAtomValue, useSetAtom } from 'jotai';
+import { useTimestampFormatter } from '../../../hooks/useTimestampFormatter';
 import { NOTIFICATION_SOUND_MAP } from '../../../utils/notificationSounds';
 import { SequenceCard } from '../../../components/sequence-card';
 import { SequenceCardStyle } from '../styles.css';
@@ -139,6 +140,7 @@ const SNOOZE_PRESETS: Array<{ label: string; resolve: (now: number) => number }>
 // Cross-platform "pause notifications" — sets a snooze instant that the
 // notification gate (ClientNonUIFeatures) reads to suppress alerts + sounds.
 function PauseNotifications() {
+  const { prefs } = useTimestampFormatter();
   const snoozeUntil = useAtomValue(notificationSnoozeUntilAtom);
   const setSnoozeUntil = useSetAtom(notificationSnoozeUntilAtom);
   // While paused, tick so the status flips to "on" the moment the snooze lapses.
@@ -155,7 +157,7 @@ function PauseNotifications() {
     ? 'Notifications are on.'
     : snoozeUntil >= SNOOZE_INDEFINITE
       ? 'Paused until you resume.'
-      : `Paused until ${formatFriendlyDateTime(snoozeUntil)}.`;
+      : `Paused until ${formatFriendlyDateTime(snoozeUntil, prefs)}.`;
 
   return (
     <SettingTile

src/app/hooks/useTimestampFormatter.ts

@@ -0,0 +1,28 @@
+import { useCallback, useMemo } from 'react';
+import { useSetting } from '../state/hooks/settings';
+import { settingsAtom } from '../state/settings';
+import {
+  TimestampStyle,
+  formatShortAge,
+  formatTimestamp,
+  TimestampPrefs,
+} from '../utils/formatTimestamp';
+
+/**
+ * [Gitea #139] Timestamp formatting bound to the user's clock/date settings.
+ * `format(ts)` is the everyday "auto" style; pass a style for the others.
+ */
+export function useTimestampFormatter() {
+  const [hour24Clock] = useSetting(settingsAtom, 'hour24Clock');
+  const [dateFormatString] = useSetting(settingsAtom, 'dateFormatString');
+  const prefs = useMemo<TimestampPrefs>(
+    () => ({ hour24Clock, dateFormatString }),
+    [hour24Clock, dateFormatString],
+  );
+  const format = useCallback(
+    (ts: number, style: TimestampStyle = 'auto') => formatTimestamp(ts, prefs, style),
+    [prefs],
+  );
+  const shortAge = useCallback((ts: number) => formatShortAge(ts, prefs), [prefs]);
+  return { format, shortAge, prefs };
+}

src/app/utils/a11y.test.ts

@@ -2,27 +2,29 @@ import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import dayjs from 'dayjs';
 import { messageAriaLabel } from './a11y';
-import { timeDayMonthYear, timeHourMinute } from './time';
 
 test('messageAriaLabel composes sender, date and time (24h)', () => {
   const ts = dayjs('2026-07-01T14:30:00').valueOf();
   assert.equal(
-    messageAriaLabel('Alice', ts, true),
+    messageAriaLabel('Alice', ts, { hour24Clock: true, dateFormatString: 'D MMM YYYY' }),
-    `Alice, ${timeDayMonthYear(ts)} ${timeHourMinute(ts, true)}`,
+    'Alice, 1 Jul 2026 14:30',
   );
 });
 
-test('messageAriaLabel honours the 12-hour clock preference', () => {
+test('messageAriaLabel honours the 12-hour clock and date-format preferences', () => {
   const ts = dayjs('2026-07-01T14:30:00').valueOf();
   assert.equal(
-    messageAriaLabel('Bob', ts, false),
+    messageAriaLabel('Bob', ts, { hour24Clock: false, dateFormatString: 'MM/DD/YYYY' }),
-    `Bob, ${timeDayMonthYear(ts)} ${timeHourMinute(ts, false)}`,
+    'Bob, 07/01/2026 02:30 PM',
   );
 });
 
 test('messageAriaLabel keeps the sender name verbatim as plain text', () => {
   const ts = dayjs('2026-07-01T09:05:00').valueOf();
-  const label = messageAriaLabel('@user:example.org', ts, true);
+  const label = messageAriaLabel('@user:example.org', ts, {
+    hour24Clock: true,
+    dateFormatString: '',
+  });
   assert.ok(label.startsWith('@user:example.org, '));
   assert.ok(!label.includes('<'));
 });

src/app/utils/a11y.ts

@@ -1,4 +1,4 @@
-import { timeDayMonthYear, timeHourMinute } from './time';
+import { TimestampPrefs, formatTimestamp } from './formatTimestamp';
 
 /**
  * Builds a plain-text accessible label for a message row, used when the
@@ -7,8 +7,8 @@ import { timeDayMonthYear, timeHourMinute } from './time';
  *
  * @param sender - Sender display name (already resolved to a human string).
  * @param ts - Message origin timestamp in milliseconds.
- * @param hour24Clock - Whether to format the time using a 24-hour clock.
+ * @param prefs - The user's clock/date preferences.
- * @returns A label such as `Alice, 1 July 2026 14:30`.
+ * @returns A label such as `Alice, 1 Jul 2026 14:30`.
  */
-export const messageAriaLabel = (sender: string, ts: number, hour24Clock: boolean): string =>
+export const messageAriaLabel = (sender: string, ts: number, prefs: TimestampPrefs): string =>
-  `${sender}, ${timeDayMonthYear(ts)} ${timeHourMinute(ts, hour24Clock)}`;
+  `${sender}, ${formatTimestamp(ts, prefs, 'dateTime')}`;

src/app/utils/datetimeInput.test.ts

@@ -55,16 +55,22 @@ test('formatFriendlyDateTime: uses Today/Tomorrow/date prefixes', () => {
   const tomorrow = new Date(2026, 0, 6, 9, 0).getTime();
   const nextWeek = new Date(2026, 0, 12, 9, 0).getTime();
 
-  assert.ok(formatFriendlyDateTime(laterToday, now).startsWith('Today at '));
+  const prefs = { hour24Clock: true, dateFormatString: 'D MMM YYYY' };
-  assert.ok(formatFriendlyDateTime(tomorrow, now).startsWith('Tomorrow at '));
+  assert.equal(formatFriendlyDateTime(laterToday, prefs, now), 'Today at 15:30');
-  const other = formatFriendlyDateTime(nextWeek, now);
+  assert.equal(formatFriendlyDateTime(tomorrow, prefs, now), 'Tomorrow at 09:00');
-  assert.ok(!other.startsWith('Today'));
+  assert.equal(formatFriendlyDateTime(nextWeek, prefs, now), '12 Jan 2026 at 09:00');
-  assert.ok(!other.startsWith('Tomorrow'));
+  assert.equal(
-  assert.ok(other.includes(' at '));
+    formatFriendlyDateTime(nextWeek, { hour24Clock: false, dateFormatString: 'MM/DD/YYYY' }, now),
+    '01/12/2026 at 09:00 AM',
+  );
 });
 
 test('formatFriendlyDateTime: Tomorrow rolls over month/year boundaries', () => {
   const nye = new Date(2026, 11, 31, 23, 0).getTime();
   const jan1 = new Date(2027, 0, 1, 9, 0).getTime();
-  assert.ok(formatFriendlyDateTime(jan1, nye).startsWith('Tomorrow at '));
+  assert.ok(
+    formatFriendlyDateTime(jan1, { hour24Clock: true, dateFormatString: '' }, nye).startsWith(
+      'Tomorrow at ',
+    ),
+  );
 });

src/app/utils/datetimeInput.ts

@@ -1,5 +1,6 @@
 import { CSSProperties } from 'react';
 import { color as foldsColor, config as foldsConfig } from 'folds';
+import { TimestampPrefs, dayWord, formatDate, formatTime } from './formatTimestamp';
 
 const pad = (n: number): string => String(n).padStart(2, '0');
 
@@ -23,21 +24,17 @@ export function parseLocalDateTime(dateValue: string, timeValue: string): Date |
   return Number.isNaN(dt.getTime()) ? null : dt;
 }
 
-// Human-friendly absolute time: "Today at 3:00 PM", "Tomorrow at 9:00 AM", or
+// Human-friendly absolute time for scheduled things: "Today at 03:00 PM",
-// "1/5/2026 at 3:00 PM". `now` is injectable so the relative-day logic is testable.
+// "Tomorrow at 09:00 AM", "Mon at 09:00", or "12 Jan 2026 at 09:00" — the
-export function formatFriendlyDateTime(ts: number, now: number = Date.now()): string {
+// shared day-word rules and the user's clock/date preferences (#139). `now` is
-  const date = new Date(ts);
+// injectable so the relative-day logic is testable.
-  const nowDate = new Date(now);
+export function formatFriendlyDateTime(
-  const sameDay = (a: Date, b: Date): boolean =>
+  ts: number,
-    a.getFullYear() === b.getFullYear() &&
+  prefs: TimestampPrefs,
-    a.getMonth() === b.getMonth() &&
+  now: number = Date.now(),
-    a.getDate() === b.getDate();
+): string {
-  const tomorrow = new Date(nowDate);
+  const day = dayWord(ts, now) ?? formatDate(ts, prefs);
-  tomorrow.setDate(tomorrow.getDate() + 1);
+  return `${day} at ${formatTime(ts, prefs)}`;
-  const timeStr = date.toLocaleTimeString(undefined, { hour: '2-digit', minute: '2-digit' });
-  if (sameDay(date, nowDate)) return `Today at ${timeStr}`;
-  if (sameDay(date, tomorrow)) return `Tomorrow at ${timeStr}`;
-  return `${date.toLocaleDateString()} at ${timeStr}`;
 }
 
 // Shared style for date/time <input>s — matches the app's surface tokens and

src/app/utils/formatTimestamp.test.ts

@@ -0,0 +1,96 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  formatDayDivider,
+  formatRelativeAge,
+  formatShortAge,
+  formatTimestamp,
+} from './formatTimestamp';
+
+// Fri 18 Sep 2026 14:05 local.
+const now = new Date(2026, 8, 18, 14, 5).getTime();
+const at = (y: number, m: number, d: number, h = 21, min = 14) =>
+  new Date(y, m - 1, d, h, min).getTime();
+const p12 = { hour24Clock: false, dateFormatString: 'D MMM YYYY' };
+const p24 = { hour24Clock: true, dateFormatString: 'YYYY-MM-DD' };
+
+describe('formatTimestamp', () => {
+  it('today → time only', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 18, 9, 3), p12, 'auto', now), '09:03 AM');
+    assert.equal(formatTimestamp(at(2026, 9, 18, 9, 3), p24, 'auto', now), '09:03');
+  });
+
+  it('yesterday / tomorrow → day word + time', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 17), p24, 'auto', now), 'Yesterday 21:14');
+    assert.equal(formatTimestamp(at(2026, 9, 19), p24, 'auto', now), 'Tomorrow 21:14');
+    // Just before midnight yesterday is still yesterday, not "hours ago".
+    assert.equal(formatTimestamp(at(2026, 9, 17, 23, 59), p24, 'auto', now), 'Yesterday 23:59');
+  });
+
+  it('within the last week → weekday + time', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 14), p24, 'auto', now), 'Mon 21:14');
+    assert.equal(formatTimestamp(at(2026, 9, 12), p24, 'auto', now), 'Sat 21:14');
+  });
+
+  it('a week or more → date + time in the user format', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 11), p24, 'auto', now), '2026-09-11 21:14');
+    assert.equal(formatTimestamp(at(2025, 1, 2), p12, 'auto', now), '2 Jan 2025 09:14 PM');
+    assert.equal(formatTimestamp(at(2026, 9, 25), p12, 'auto', now), '25 Sep 2026 09:14 PM');
+  });
+
+  it('autoDate never shows the time', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 18), p12, 'autoDate', now), 'Today');
+    assert.equal(formatTimestamp(at(2026, 9, 17), p12, 'autoDate', now), 'Yesterday');
+    assert.equal(formatTimestamp(at(2026, 9, 15), p12, 'autoDate', now), 'Tue');
+    assert.equal(formatTimestamp(at(2026, 1, 15), p12, 'autoDate', now), '15 Jan 2026');
+  });
+
+  it('fixed styles ignore the relative day', () => {
+    assert.equal(formatTimestamp(at(2026, 9, 18), p12, 'time', now), '09:14 PM');
+    assert.equal(formatTimestamp(at(2026, 9, 18), p12, 'date', now), '18 Sep 2026');
+    assert.equal(formatTimestamp(at(2026, 9, 18), p24, 'dateTime', now), '2026-09-18 21:14');
+  });
+
+  it('falls back to a default date format when the preference is empty', () => {
+    assert.equal(
+      formatTimestamp(at(2026, 1, 15), { hour24Clock: true, dateFormatString: '' }, 'date', now),
+      '15 Jan 2026',
+    );
+  });
+});
+
+describe('formatShortAge', () => {
+  it('minutes and hours today', () => {
+    assert.equal(formatShortAge(now - 20_000, p12, now), 'now');
+    assert.equal(formatShortAge(now - 5 * 60_000, p12, now), '5m');
+    assert.equal(formatShortAge(now - 3 * 3_600_000, p12, now), '3h');
+  });
+
+  it('day words, then a short date (year dropped when current)', () => {
+    assert.equal(formatShortAge(at(2026, 9, 17, 23, 0), p12, now), 'Yesterday');
+    assert.equal(formatShortAge(at(2026, 9, 14), p12, now), 'Mon');
+    assert.equal(formatShortAge(at(2026, 3, 2), p12, now), '2 Mar');
+    assert.equal(formatShortAge(at(2026, 3, 2), p24, now), '03-02');
+    assert.equal(formatShortAge(at(2025, 3, 2), p12, now), '2 Mar 2025');
+  });
+});
+
+describe('formatRelativeAge', () => {
+  it('steps through minutes, hours, days, then the date', () => {
+    assert.equal(formatRelativeAge(now - 10_000, p12, now), 'just now');
+    assert.equal(formatRelativeAge(now - 7 * 60_000, p12, now), '7m ago');
+    assert.equal(formatRelativeAge(now - 5 * 3_600_000, p12, now), '5h ago');
+    assert.equal(formatRelativeAge(at(2026, 9, 17, 8), p12, now), 'yesterday');
+    assert.equal(formatRelativeAge(at(2026, 9, 15, 8), p12, now), '3d ago');
+    assert.equal(formatRelativeAge(at(2026, 9, 1, 8), p24, now), '2026-09-01');
+  });
+});
+
+describe('formatDayDivider', () => {
+  it('uses the full weekday inside the last week', () => {
+    assert.equal(formatDayDivider(at(2026, 9, 18), p12, now), 'Today');
+    assert.equal(formatDayDivider(at(2026, 9, 17), p12, now), 'Yesterday');
+    assert.equal(formatDayDivider(at(2026, 9, 14), p12, now), 'Monday');
+    assert.equal(formatDayDivider(at(2026, 9, 11), p12, now), '11 Sep 2026');
+  });
+});

src/app/utils/formatTimestamp.ts

@@ -0,0 +1,117 @@
+import dayjs from 'dayjs';
+
+/**
+ * [Gitea #139] One place that turns a timestamp into words, honouring the
+ * user's 12/24 h clock and date-format preferences everywhere.
+ *
+ * Rules for the `auto` styles, relative to `now`:
+ *   today            → "21:14"
+ *   yesterday        → "Yesterday 21:14"
+ *   tomorrow         → "Tomorrow 21:14"        (scheduled sends, reminders)
+ *   last 6 days      → "Mon 21:14"
+ *   older / further  → "5 Sep 2026 21:14"      (date per `dateFormatString`)
+ */
+export type TimestampPrefs = {
+  hour24Clock: boolean;
+  dateFormatString: string;
+};
+
+export type TimestampStyle =
+  /** Time for today, day word + time for nearby days, date + time otherwise. */
+  | 'auto'
+  /** Like `auto` but never the time: "Today", "Yesterday", "Mon", "5 Sep 2026". */
+  | 'autoDate'
+  /** Always the clock time. */
+  | 'time'
+  /** Always the date per `dateFormatString`. */
+  | 'date'
+  /** Always date + time. */
+  | 'dateTime';
+
+const DEFAULT_DATE_FORMAT = 'D MMM YYYY';
+
+const dateFormat = (prefs: TimestampPrefs) => prefs.dateFormatString || DEFAULT_DATE_FORMAT;
+
+export const formatTime = (ts: number, prefs: Pick<TimestampPrefs, 'hour24Clock'>): string =>
+  dayjs(ts).format(prefs.hour24Clock ? 'HH:mm' : 'hh:mm A');
+
+export const formatDate = (ts: number, prefs: TimestampPrefs): string =>
+  dayjs(ts).format(dateFormat(prefs));
+
+/** Whole days between the start of `ts`'s day and the start of `now`'s day (negative = future). */
+export const dayDistance = (ts: number, now: number): number =>
+  dayjs(now).startOf('day').diff(dayjs(ts).startOf('day'), 'day');
+
+/** "Today" / "Yesterday" / "Tomorrow" / "Mon" for nearby days, else undefined. */
+export const dayWord = (ts: number, now: number): string | undefined => {
+  const d = dayDistance(ts, now);
+  if (d === 0) return 'Today';
+  if (d === 1) return 'Yesterday';
+  if (d === -1) return 'Tomorrow';
+  if (d > 1 && d < 7) return dayjs(ts).format('ddd');
+  return undefined;
+};
+
+export function formatTimestamp(
+  ts: number,
+  prefs: TimestampPrefs,
+  style: TimestampStyle = 'auto',
+  now: number = Date.now(),
+): string {
+  const time = formatTime(ts, prefs);
+  if (style === 'time') return time;
+  const date = formatDate(ts, prefs);
+  if (style === 'date') return date;
+  if (style === 'dateTime') return `${date} ${time}`;
+
+  const word = dayWord(ts, now);
+  if (style === 'autoDate') return word ?? date;
+  if (word === 'Today') return time;
+  return `${word ?? date} ${time}`;
+}
+
+/** Short relative age for dense lists: "now", "5m", "3h", "Yesterday", "Mon", "5 Sep". */
+export function formatShortAge(
+  ts: number,
+  prefs: TimestampPrefs,
+  now: number = Date.now(),
+): string {
+  const diffMin = Math.floor((now - ts) / 60_000);
+  if (diffMin < 60) return diffMin < 1 ? 'now' : `${diffMin}m`;
+  const diffHours = Math.floor(diffMin / 60);
+  if (diffHours < 24 && dayDistance(ts, now) === 0) return `${diffHours}h`;
+  const word = dayWord(ts, now);
+  if (word && word !== 'Today') return word;
+  // Same year: drop the year from the user's format for brevity.
+  const sameYear = dayjs(ts).year() === dayjs(now).year();
+  const fmt = dateFormat(prefs);
+  return dayjs(ts).format(sameYear ? fmt.replace(/[-/.\s]*Y{2,4}[-/.\s]*/, ' ').trim() : fmt);
+}
+
+/** Conversational age for list rows: "just now", "5m ago", "3h ago", "yesterday", "3d ago", then the date. */
+export function formatRelativeAge(
+  ts: number,
+  prefs: TimestampPrefs,
+  now: number = Date.now(),
+): string {
+  const diffMin = Math.floor((now - ts) / 60_000);
+  if (diffMin < 1) return 'just now';
+  if (diffMin < 60) return `${diffMin}m ago`;
+  const diffHours = Math.floor(diffMin / 60);
+  if (diffHours < 24) return `${diffHours}h ago`;
+  const days = dayDistance(ts, now);
+  if (days === 1) return 'yesterday';
+  if (days < 7) return `${days}d ago`;
+  return formatDate(ts, prefs);
+}
+
+/** Timeline day divider: "Today", "Yesterday", "Monday" (last 6 days), else the date. */
+export function formatDayDivider(
+  ts: number,
+  prefs: TimestampPrefs,
+  now: number = Date.now(),
+): string {
+  const d = dayDistance(ts, now);
+  if (d > 1 && d < 7) return dayjs(ts).format('dddd');
+  return formatTimestamp(ts, prefs, 'autoDate', now);
+}