diff --git a/ui/src/pages/SubstratePage.tsx b/ui/src/pages/SubstratePage.tsx
index d3e8dc5c74..d9f822c075 100644
--- a/ui/src/pages/SubstratePage.tsx
+++ b/ui/src/pages/SubstratePage.tsx
@@ -692,25 +692,74 @@ function SectionSearch({
 
 const PAGE_SIZE = 25;
 
-function PageAge({ computedAt }: { computedAt?: string }) {
+/**
+ * When the list was read, as a clock time rather than a running age: an age that ticks
+ * twice a second pulls the eye off the rows while saying nothing new.
+ *
+ * While polling, a list with no new read for `STALLED_AFTER_TICKS` intervals adds how
+ * long it has gone without one, in the warning colour. That is the stall the old age
+ * showed, now shown only when it is happening.
+ */
+function PageAge({ computedAt, pollMs }: { computedAt?: string; pollMs?: number }) {
   const theme = useTheme();
-  const age = useDataAge(computedAt);
-  return <Text css={{ color: theme.color.textMuted, fontSize: 12 }}>{age}</Text>;
+  const stalledMs = useStalledFor(computedAt, pollMs);
+  const at = readAt(computedAt);
+  if (stalledMs === undefined) {
+    return <Text css={{ color: theme.color.textMuted, fontSize: 12 }}>{at}</Text>;
+  }
+  return (
+    <Text css={{ color: theme.color.warning, fontSize: 12 }}>
+      {`${at}, ${elapsed(stalledMs)} ago`}
+    </Text>
+  );
 }
 
-function useDataAge(computedAt: string | undefined): string {
-  const [now, setNow] = useState(() => Date.now());
+const STALLED_AFTER_TICKS = 3;
+// A floor, so a half-second interval does not call one slow read a stall.
+const STALLED_FLOOR_MS = 5_000;
+
+/**
+ * How long a polled list has gone without a new read, once that is a stall.
+ *
+ * Measured on the browser's clock from when `computedAt` last changed, not from
+ * `computedAt` itself, so a skewed server clock cannot raise it.
+ */
+function useStalledFor(computedAt: string | undefined, pollMs: number | undefined) {
+  const [stall, setStall] = useState<{ key?: string; ms: number }>();
+
   useEffect(() => {
-    const timer = window.setInterval(() => setNow(Date.now()), 500);
+    if (pollMs === undefined) return;
+    const sinceMs = Date.now();
+    const limitMs = Math.max(STALLED_AFTER_TICKS * pollMs, STALLED_FLOOR_MS);
+    const timer = window.setInterval(() => {
+      const ms = Date.now() - sinceMs;
+      setStall(ms >= limitMs ? { key: computedAt, ms } : undefined);
+    }, 1_000);
     return () => window.clearInterval(timer);
-  }, []);
+  }, [computedAt, pollMs]);
 
+  // A stall belongs to the read it was measured against; a new read clears it at once.
+  return pollMs !== undefined && stall !== undefined && stall.key === computedAt
+    ? stall.ms
+    : undefined;
+}
+
+function readAt(computedAt: string | undefined): string {
   if (!computedAt) return "";
-  const at = new Date(computedAt).getTime();
-  if (Number.isNaN(at)) return "";
-  const seconds = Math.max(0, (now - at) / 1000);
-  if (seconds < 1) return "read just now";
-  return `read ${seconds.toFixed(1)}s ago`;
+  const at = new Date(computedAt);
+  if (Number.isNaN(at.getTime())) return "";
+  return `Read at ${at.toLocaleTimeString([], {
+    hour: "numeric",
+    minute: "2-digit",
+    second: "2-digit",
+  })}`;
+}
+
+/** `12s`, `3m 05s`. */
+function elapsed(ms: number): string {
+  const whole = Math.floor(ms / 1_000);
+  if (whole < 60) return `${whole}s`;
+  return `${Math.floor(whole / 60)}m ${String(whole % 60).padStart(2, "0")}s`;
 }
 
 function PageWarning({ message, testId }: { message: string; testId: string }) {
@@ -1484,7 +1533,7 @@ export function SubstratePage() {
               "& > [data-testid$='-pages']": { marginTop: 0 },
             }}
           >
-            <PageAge computedAt={actors.data?.computedAt} />
+            <PageAge computedAt={actors.data?.computedAt} pollMs={isTicking ? pollMs : undefined} />
 
             <PageControls
               testId="substrate-actors-pages"
@@ -1562,7 +1611,7 @@ export function SubstratePage() {
               "& > [data-testid$='-pages']": { marginTop: 0 },
             }}
           >
-            <PageAge computedAt={workers.data?.computedAt} />
+            <PageAge computedAt={workers.data?.computedAt} pollMs={isTicking ? pollMs : undefined} />
 
             <PageControls
               testId="substrate-workers-pages"
diff --git a/ui/src/pages/substrateReadAge.test.tsx b/ui/src/pages/substrateReadAge.test.tsx
new file mode 100644
index 0000000000..6452772c30
--- /dev/null
+++ b/ui/src/pages/substrateReadAge.test.tsx
@@ -0,0 +1,45 @@
+import { act, fireEvent, render, screen } from "@testing-library/react";
+import { ThemeProvider } from "@emotion/react";
+import { MemoryRouter } from "react-router-dom";
+import { SWRConfig } from "swr";
+import { afterEach, expect, it, vi } from "vitest";
+import { createRouterTransport } from "@connectrpc/connect";
+import { timestampFromDate } from "@bufbuild/protobuf/wkt";
+import { SystemService } from "@/generated/kagent/api/v1/system_pb";
+import { setApiTransport } from "@/api/transport";
+import { themeFor } from "@/theme/theme";
+import { SubstratePage } from "./SubstratePage";
+
+afterEach(() => {
+  setApiTransport(undefined);
+  vi.useRealTimers();
+});
+
+// The lists answer once, then hang: polling keeps asking and no new read lands.
+it("shows how long a polled list has gone without a new read", async () => {
+  vi.useFakeTimers({ toFake: ["setInterval", "clearInterval", "Date"] });
+  const hang = () => new Promise<never>(() => {});
+  let actorReads = 0;
+  setApiTransport(createRouterTransport(({ service }) => service(SystemService, {
+    listNamespaces: () => ({}),
+    getSubstrateSummary: () => ({}),
+    listSubstrateActors: () =>
+      actorReads++ === 0 ? { computedAt: timestampFromDate(new Date()) } : hang(),
+    listSubstrateWorkers: () => ({ computedAt: timestampFromDate(new Date()) }),
+  })));
+  render(<ThemeProvider theme={themeFor("dark")}>
+    <SWRConfig value={{ provider: () => new Map(), shouldRetryOnError: false }}>
+      <MemoryRouter><SubstratePage /></MemoryRouter>
+    </SWRConfig>
+  </ThemeProvider>);
+
+  const [actorsAge] = await screen.findAllByText(/^Read at /);
+  expect(actorsAge).not.toHaveTextContent(/ago$/);
+
+  fireEvent.click(screen.getByTestId("substrate-poll-toggle"));
+  await act(async () => {
+    vi.advanceTimersByTime(8_000);
+  });
+
+  expect(actorsAge).toHaveTextContent(/^Read at .+, \d+s ago$/);
+});