diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index 4b223bf35..92da5b625 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -104,6 +104,7 @@ export interface MessagePartProps {
   hideDetails?: boolean
   defaultOpen?: boolean
   showAssistantCopyPartID?: string | null
+  turnDurationMs?: number
 }
 
 export type PartComponent = Component<MessagePartProps>
@@ -275,6 +276,7 @@ function renderable(part: PartType) {
 export function AssistantParts(props: {
   messages: AssistantMessage[]
   showAssistantCopyPartID?: string | null
+  turnDurationMs?: number
   working?: boolean
 }) {
   const data = useData()
@@ -365,6 +367,7 @@ export function AssistantParts(props: {
                   part={entry().part}
                   message={entry().message}
                   showAssistantCopyPartID={props.showAssistantCopyPartID}
+                  turnDurationMs={props.turnDurationMs}
                 />
               )}
             </Show>
@@ -849,6 +852,7 @@ export function Part(props: MessagePartProps) {
         hideDetails={props.hideDetails}
         defaultOpen={props.defaultOpen}
         showAssistantCopyPartID={props.showAssistantCopyPartID}
+        turnDurationMs={props.turnDurationMs}
       />
     </Show>
   )
@@ -1060,8 +1064,12 @@ PART_MAPPING["text"] = function TextPartDisplay(props) {
     if (props.message.role !== "assistant") return ""
     const message = props.message as AssistantMessage
     const completed = message.time.completed
-    if (typeof completed !== "number") return ""
-    const ms = completed - message.time.created
+    const ms =
+      typeof props.turnDurationMs === "number"
+        ? props.turnDurationMs
+        : typeof completed === "number"
+          ? completed - message.time.created
+          : -1
     if (!(ms >= 0)) return ""
     const total = Math.round(ms / 1000)
     if (total < 60) return `${total}s`
diff --git a/packages/ui/src/components/session-turn.tsx b/packages/ui/src/components/session-turn.tsx
index 2aed8279e..aa2769280 100644
--- a/packages/ui/src/components/session-turn.tsx
+++ b/packages/ui/src/components/session-turn.tsx
@@ -247,6 +247,21 @@ export function SessionTurn(
     if (working()) return null
     return showAssistantCopyPartID() ?? null
   })
+  const turnDurationMs = createMemo(() => {
+    const start = message()?.time.created
+    if (typeof start !== "number") return undefined
+
+    const end = assistantMessages().reduce<number | undefined>((max, item) => {
+      const completed = item.time.completed
+      if (typeof completed !== "number") return max
+      if (max === undefined) return completed
+      return Math.max(max, completed)
+    }, undefined)
+
+    if (typeof end !== "number") return undefined
+    if (end < start) return undefined
+    return end - start
+  })
   const assistantVisible = createMemo(() =>
     assistantMessages().reduce((count, message) => {
       const parts = list(data.store.part?.[message.id], emptyParts)
@@ -290,6 +305,7 @@ export function SessionTurn(
                     <AssistantParts
                       messages={assistantMessages()}
                       showAssistantCopyPartID={assistantCopyPartID()}
+                      turnDurationMs={turnDurationMs()}
                       working={working()}
                     />
                   </div>