diff --git a/src/features/message/MessageRenderer.tsx b/src/features/message/MessageRenderer.tsx
index 92a26d62..0db992f9 100644
--- a/src/features/message/MessageRenderer.tsx
+++ b/src/features/message/MessageRenderer.tsx
@@ -37,7 +37,7 @@ import type {
   AssistantMessageInfo,
 } from '../../types/message'
 import { isToolPart, isVisibleReasoningPart, isVisibleTextPart } from '../../types/message'
-import { formatDuration, formatCompletedAt } from '../../utils/formatUtils'
+import { formatDuration, formatCompletedAt, formatDetailedDateTime } from '../../utils/formatUtils'
 
 interface MessageRendererProps {
   message: Message
@@ -376,6 +376,7 @@ const AssistantMessageView = memo(function AssistantMessageView({
   forkMessageId?: string
   onEnsureParts?: (messageId: string) => void
 }) {
+  const { t } = useTranslation('message')
   const { parts, isStreaming, info } = message
   const { stepFinishDisplay, completedAtFormat } = useTheme()
 
@@ -513,9 +514,13 @@ const AssistantMessageView = memo(function AssistantMessageView({
       {messageError && <MessageErrorView error={messageError} />}
 
       {(showTurnDurationFooter || showCompletedAtFooter) && (
-        <div className="flex items-center gap-3 text-[length:var(--fs-xxs)] text-text-500 pl-5 py-0.5">
-          {showTurnDurationFooter && <span>{formatDuration(turnDuration!)} total</span>}
-          {showCompletedAtFooter && <span>{formatCompletedAt(completed!, completedAtFormat)}</span>}
+        <div className="flex items-center gap-3 py-0.5 text-[length:var(--fs-xxs)] text-text-500">
+          {showTurnDurationFooter && (
+            <span>{t('stepFinish.totalDuration', { duration: formatDuration(turnDuration!) })}</span>
+          )}
+          {showCompletedAtFooter && (
+            <span title={formatDetailedDateTime(completed!)}>{formatCompletedAt(completed!, completedAtFormat)}</span>
+          )}
         </div>
       )}
 
diff --git a/src/features/message/parts/StepFinishPartView.tsx b/src/features/message/parts/StepFinishPartView.tsx
index a8aeb611..642937ec 100644
--- a/src/features/message/parts/StepFinishPartView.tsx
+++ b/src/features/message/parts/StepFinishPartView.tsx
@@ -2,7 +2,13 @@ import { memo } from 'react'
 import { useTranslation } from 'react-i18next'
 import { useTheme } from '../../../hooks/useTheme'
 import type { StepFinishPart } from '../../../types/message'
-import { formatNumber, formatCost, formatDuration, formatCompletedAt } from '../../../utils/formatUtils'
+import {
+  formatNumber,
+  formatCost,
+  formatDuration,
+  formatCompletedAt,
+  formatDetailedDateTime,
+} from '../../../utils/formatUtils'
 
 interface StepFinishPartViewProps {
   part: StepFinishPart
@@ -68,7 +74,9 @@ export const StepFinishPartView = memo(function StepFinishPartView({
       {show.turnDuration && turnDuration != null && turnDuration > 0 && (
         <span>{t('stepFinish.totalDuration', { duration: formatDuration(turnDuration) })}</span>
       )}
-      {show.completedAt && completedAt != null && <span>{formatCompletedAt(completedAt, completedAtFormat)}</span>}
+      {show.completedAt && completedAt != null && (
+        <span title={formatDetailedDateTime(completedAt)}>{formatCompletedAt(completedAt, completedAtFormat)}</span>
+      )}
     </div>
   )
 })
diff --git a/src/utils/formatUtils.test.ts b/src/utils/formatUtils.test.ts
index c8d6e5c4..e619a03c 100644
--- a/src/utils/formatUtils.test.ts
+++ b/src/utils/formatUtils.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { formatCompletedAt, formatDateTime, formatDuration, formatTime } from './formatUtils'
+import { formatCompletedAt, formatDateTime, formatDetailedDateTime, formatDuration, formatTime } from './formatUtils'
 
 describe('formatDuration', () => {
   it('formats milliseconds and seconds', () => {
@@ -34,6 +34,11 @@ describe('completed time formatting', () => {
     expect(formatDateTime(ms)).toBe('2026-04-17 10:30')
   })
 
+  it('formats detailed local date and time with seconds', () => {
+    const ms = new Date(2026, 3, 17, 10, 30, 45).getTime()
+    expect(formatDetailedDateTime(ms)).toBe('2026-04-17 10:30:45')
+  })
+
   it('switches output based on completedAt format', () => {
     const ms = new Date(2026, 3, 17, 10, 30, 45).getTime()
     expect(formatCompletedAt(ms, 'time')).toBe('10:30')
diff --git a/src/utils/formatUtils.ts b/src/utils/formatUtils.ts
index 8fdb0e35..7c8bd950 100644
--- a/src/utils/formatUtils.ts
+++ b/src/utils/formatUtils.ts
@@ -54,6 +54,18 @@ export function formatDateTime(ms: number): string {
   return `${y}-${mon}-${d} ${formatTime(ms)}`
 }
 
+/** Format a timestamp (ms) to local YYYY-MM-DD HH:MM:SS string for detail tooltips */
+export function formatDetailedDateTime(ms: number): string {
+  const date = new Date(ms)
+  const y = date.getFullYear().toString().padStart(4, '0')
+  const mon = (date.getMonth() + 1).toString().padStart(2, '0')
+  const d = date.getDate().toString().padStart(2, '0')
+  const h = date.getHours().toString().padStart(2, '0')
+  const m = date.getMinutes().toString().padStart(2, '0')
+  const s = date.getSeconds().toString().padStart(2, '0')
+  return `${y}-${mon}-${d} ${h}:${m}:${s}`
+}
+
 /** Format completed time according to the selected display mode */
 export function formatCompletedAt(ms: number, format: CompletedAtFormat): string {
   return format === 'dateTime' ? formatDateTime(ms) : formatTime(ms)