diff --git a/assets/js/hooks/Mapper/components/map/helpers/signatureAge.test.ts b/assets/js/hooks/Mapper/components/map/helpers/signatureAge.test.ts
index 20599df8f..a1d4da76e 100644
--- a/assets/js/hooks/Mapper/components/map/helpers/signatureAge.test.ts
+++ b/assets/js/hooks/Mapper/components/map/helpers/signatureAge.test.ts
@@ -15,13 +15,6 @@ const sig = (overrides: Partial<SystemSignature> = {}): SystemSignature => ({
 
 const hoursAgo = (h: number) => new Date(NOW - h * HOUR).toISOString();
 
-// The format the server actually puts on the wire: `Calendar.strftime(dt,
-// "%Y/%m/%d %H:%M:%S")` in `get_system_signatures/1`. It is UTC, but carries
-// nothing that says so. Fixtures built with `toISOString()` are ISO-8601 with a
-// `Z`, so they never exercised this path.
-const serverHoursAgo = (h: number) =>
-  new Date(NOW - h * HOUR).toISOString().replace(/-/g, '/').slice(0, 19).replace('T', ' ');
-
 describe('computeSignatureAge', () => {
   it('reports no age when the system has no signatures at all', () => {
     expect(computeSignatureAge([], NOW).signatureAgeHours).toBe(-1);
@@ -87,49 +80,12 @@ describe('computeSignatureAge', () => {
     expect(newestUpdatedAt).toBe(NOW - 7 * HOUR);
   });
 
-  // The reported bug: west of UTC, `new Date('2026/08/09 10:00:00')` resolves to
-  // 10:00 *local*, which is later than the real instant, so every age landed in
-  // the `Math.max(0, ...)` clamp and the bookmark read 0h for hours on end.
-  it('reads the zone-less server timestamp format as UTC', () => {
-    const sigs = [sig({ updated_at: serverHoursAgo(6) })];
-
-    expect(computeSignatureAge(sigs, NOW).signatureAgeHours).toBe(6);
-  });
-
-  it('reads the server format on the inserted_at fallback too', () => {
-    const sigs = [sig({ inserted_at: serverHoursAgo(9) })];
-
-    expect(computeSignatureAge(sigs, NOW).signatureAgeHours).toBe(9);
-  });
-
   it('still reads an ISO-8601 timestamp with an explicit zone', () => {
     const sigs = [sig({ updated_at: hoursAgo(6) })];
 
     expect(computeSignatureAge(sigs, NOW).signatureAgeHours).toBe(6);
   });
 
-  // `Date.UTC` normalises rather than rejects, so without a round-trip check
-  // these build a real-looking instant out of garbage — indistinguishable, to
-  // every caller, from a timestamp the server actually sent.
-  it.each([
-    ['a month that does not exist', '2026/13/09 10:00:00'],
-    ['a day the month does not have', '2026/02/31 10:00:00'],
-    ['an hour past the end of the day', '2026/08/09 99:99:99'],
-    ['trailing text after a valid prefix', '2026/08/09 10:00:00 and then some'],
-  ])('falls back to inserted_at for %s', (_label, updated_at) => {
-    const sigs = [sig({ updated_at, inserted_at: serverHoursAgo(4) })];
-
-    expect(computeSignatureAge(sigs, NOW).signatureAgeHours).toBe(4);
-  });
-
-  it('accepts the last second of a leap day', () => {
-    const sigs = [sig({ updated_at: '2024/02/29 23:59:59' })];
-
-    expect(computeSignatureAge(sigs, Date.parse('2024/02/29T23:59:59Z') + HOUR).newestUpdatedAt).toBe(
-      Date.UTC(2024, 1, 29, 23, 59, 59),
-    );
-  });
-
   it('reports no age when neither timestamp will parse', () => {
     const sigs = [sig({ updated_at: 'not-a-date', inserted_at: 'also-not-a-date' })];
 
diff --git a/assets/js/hooks/Mapper/components/map/helpers/signatureAge.ts b/assets/js/hooks/Mapper/components/map/helpers/signatureAge.ts
index dc47905c5..4e9e20d73 100644
--- a/assets/js/hooks/Mapper/components/map/helpers/signatureAge.ts
+++ b/assets/js/hooks/Mapper/components/map/helpers/signatureAge.ts
@@ -50,53 +50,17 @@ export function formatSignatureAge(signatureAgeHours: number): string {
   return `${Math.floor(signatureAgeHours / DAY_HOURS)}d`;
 }
 
-/**
- * The zone-less timestamp format the LiveView puts on the wire, from
- * `Calendar.strftime(dt, "%Y/%m/%d %H:%M:%S")` in `get_system_signatures/1`.
- *
- * Anchored at both ends: an unanchored match would accept a well-formed prefix
- * followed by anything at all, which `new Date` would have rejected outright.
- */
-const SERVER_TIMESTAMP = /^(\d{4})\/(\d{2})\/(\d{2})[ T](\d{2}):(\d{2}):(\d{2})$/;
-
-/**
- * Resolves the zone-less server format as UTC, or 0 if the components do not
- * describe a real instant.
- *
- * `Date.UTC` normalises out-of-range components rather than rejecting them, so
- * month 13 becomes February of the next year and 2026/02/31 becomes March 3rd —
- * a plausible-looking timestamp built out of garbage, which is worse than no
- * timestamp at all because the caller cannot tell it apart from a real one.
- * Reading the components back off the result rejects exactly the values that
- * were normalised, which covers every out-of-range field without enumerating
- * per-field bounds or special-casing leap years.
- */
-function parseServerTimestamp(parts: RegExpExecArray): number {
-  const [, year, month, day, hour, minute, second] = parts.map(Number);
-  const ts = Date.UTC(year, month - 1, day, hour, minute, second);
-  const back = new Date(ts);
-
-  const roundTrips =
-    back.getUTCFullYear() === year &&
-    back.getUTCMonth() === month - 1 &&
-    back.getUTCDate() === day &&
-    back.getUTCHours() === hour &&
-    back.getUTCMinutes() === minute &&
-    back.getUTCSeconds() === second;
-
-  return roundTrips ? ts : 0;
-}
-
 /**
  * Parses a signature timestamp, treating anything unparseable as absent.
  *
- * The server sends UTC with nothing marking it as UTC, and `new Date` reads that
- * format as *local* time. West of UTC that puts every timestamp in the future,
- * so `now - updated_at` went negative and the age clamped to 0 — the bookmark
- * sat at "0h" no matter how long ago the system was really scanned. The offset
- * is applied explicitly here rather than by the `getTimezoneOffset()` correction
- * `TimeLeft` uses, so the value this returns is a real instant that callers can
- * compare against `Date.now()` without knowing how it was encoded.
+ * The server sends ISO-8601 with an explicit zone, so `new Date` resolves it to
+ * a real instant and this needs no correction. It previously sent UTC formatted
+ * as `%Y/%m/%d %H:%M:%S` with nothing marking it as UTC, which `new Date` read
+ * as *local* time — west of UTC that put every timestamp in the future, drove
+ * `now - updated_at` negative, and pinned the age bookmark at "0h" no matter how
+ * long ago the system was really scanned. Both readers of that format carried a
+ * `getTimezoneOffset()` correction to cancel it out; the format and the
+ * corrections were removed together, so there is one parse path again.
  *
  * `new Date('garbage').getTime()` is NaN, and NaN loses every `>` comparison,
  * so an unparseable value would otherwise be indistinguishable from "no
@@ -106,10 +70,6 @@ function parseTimestamp(value?: string | null): number {
   if (!value) {
     return 0;
   }
-  const parts = SERVER_TIMESTAMP.exec(value);
-  if (parts) {
-    return parseServerTimestamp(parts);
-  }
   const ts = new Date(value).getTime();
   return Number.isFinite(ts) ? ts : 0;
 }
diff --git a/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.test.ts b/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.test.ts
new file mode 100644
index 000000000..8497a21e8
--- /dev/null
+++ b/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.test.ts
@@ -0,0 +1,28 @@
+import { getRowBackgroundColor } from './getRowBackgroundColor';
+
+const NOW = Date.parse('2026-08-09T12:00:00Z');
+const SECOND = 1000;
+const MINUTE = 60 * SECOND;
+
+// The row highlight and `TimeLeft` both used to add `getTimezoneOffset()` to
+// *now*, cancelling out the fact that signature timestamps arrived as zone-less
+// UTC that `new Date` had read as local. Now that the server sends ISO-8601, the
+// timestamps are real instants and the correction has to be gone: west of UTC it
+// would push every age hours into the past and no row would ever highlight.
+describe('getRowBackgroundColor', () => {
+  it('highlights a signature added seconds ago', () => {
+    expect(getRowBackgroundColor(new Date(NOW - 5 * SECOND), NOW)).toContain('amber-300');
+  });
+
+  it('uses the ten-minute colour for a signature a few minutes old', () => {
+    expect(getRowBackgroundColor(new Date(NOW - 5 * MINUTE), NOW)).toContain('amber-500');
+  });
+
+  it('stops highlighting past ten minutes', () => {
+    expect(getRowBackgroundColor(new Date(NOW - 11 * MINUTE), NOW)).toBe('');
+  });
+
+  it('returns nothing without a date', () => {
+    expect(getRowBackgroundColor(undefined, NOW)).toBe('');
+  });
+});
diff --git a/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.ts b/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.ts
index 68f49c1d8..046129597 100644
--- a/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.ts
+++ b/assets/js/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/helpers/getRowBackgroundColor.ts
@@ -3,13 +3,12 @@ import {
   TIME_TEN_MINUTES,
 } from '@/hooks/Mapper/components/mapInterface/widgets/SystemSignatures/constants.ts';
 
-export const getRowBackgroundColor = (date: Date | undefined): string => {
+export const getRowBackgroundColor = (date: Date | undefined, now: number = Date.now()): string => {
   if (!date) {
     return '';
   }
 
-  const currentDate = new Date();
-  const diff = currentDate.getTime() + currentDate.getTimezoneOffset() * TIME_ONE_MINUTE - date.getTime();
+  const diff = now - date.getTime();
 
   if (diff < TIME_ONE_MINUTE) {
     return '[&_.ssc-header]:text-amber-300 [&_.ssc-header]:hover:text-amber-200 [&_.ssc-header]:font-bold';
diff --git a/assets/js/hooks/Mapper/components/ui-kit/TimeLeft/TimeLeft.tsx b/assets/js/hooks/Mapper/components/ui-kit/TimeLeft/TimeLeft.tsx
index 3ebb0ec00..140bed22f 100644
--- a/assets/js/hooks/Mapper/components/ui-kit/TimeLeft/TimeLeft.tsx
+++ b/assets/js/hooks/Mapper/components/ui-kit/TimeLeft/TimeLeft.tsx
@@ -31,7 +31,12 @@ export const TimeLeft: FC<TimeLeftProps> = ({ cDate = new Date() }) => {
 
   const update = () => {
     const currentDate = new Date();
-    const diff = currentDate.getTime() + currentDate.getTimezoneOffset() * 60000 - date.getTime();
+    // No timezone correction: `cDate` is built from a timestamp that names its
+    // own zone, so it is already a real instant. This used to add
+    // `getTimezoneOffset()` to compensate for signature timestamps arriving as
+    // zone-less UTC that `new Date` read as local time; the server now sends
+    // ISO-8601 and correcting again would reintroduce the same error, inverted.
+    const diff = currentDate.getTime() - date.getTime();
     setTimeDiff(calculateTimeDiff(diff));
   };
 
diff --git a/lib/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler.ex b/lib/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler.ex
index 2539f49a0..8309fe898 100644
--- a/lib/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler.ex
+++ b/lib/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler.ex
@@ -545,8 +545,8 @@ defmodule WandererAppWeb.MapSignaturesEventHandler do
       ])
       |> Map.put(:character_name, Map.get(character_names_map, s.character_eve_id))
       |> Map.put(:linked_system, MapEventHandler.get_system_static_info(linked_system_id))
-      |> Map.put(:inserted_at, inserted_at |> Calendar.strftime("%Y/%m/%d %H:%M:%S"))
-      |> Map.put(:updated_at, updated_at |> Calendar.strftime("%Y/%m/%d %H:%M:%S"))
+      |> Map.put(:inserted_at, DateTime.to_iso8601(inserted_at))
+      |> Map.put(:updated_at, DateTime.to_iso8601(updated_at))
     end)
   end
 
diff --git a/lib/wanderer_app_web/live/map/event_handlers/map_structures_event_handler.ex b/lib/wanderer_app_web/live/map/event_handlers/map_structures_event_handler.ex
index 662a4207f..3c13c245e 100644
--- a/lib/wanderer_app_web/live/map/event_handlers/map_structures_event_handler.ex
+++ b/lib/wanderer_app_web/live/map/event_handlers/map_structures_event_handler.ex
@@ -124,8 +124,8 @@ defmodule WandererAppWeb.MapStructuresEventHandler do
           :structure_type,
           :inherited_from_map_id
         ])
-        |> Map.update!(:inserted_at, &Calendar.strftime(&1, "%Y/%m/%d %H:%M:%S"))
-        |> Map.update!(:updated_at, &Calendar.strftime(&1, "%Y/%m/%d %H:%M:%S"))
+        |> Map.update!(:inserted_at, &DateTime.to_iso8601/1)
+        |> Map.update!(:updated_at, &DateTime.to_iso8601/1)
       end)
 
     Logger.debug(fn ->
diff --git a/test/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler_test.exs b/test/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler_test.exs
new file mode 100644
index 000000000..a245922ce
--- /dev/null
+++ b/test/wanderer_app_web/live/map/event_handlers/map_signatures_event_handler_test.exs
@@ -0,0 +1,40 @@
+defmodule WandererAppWeb.MapSignaturesEventHandlerTest do
+  use WandererApp.DataCase, async: false
+
+  alias WandererAppWeb.MapSignaturesEventHandler
+
+  describe "get_system_signatures/1" do
+    setup do
+      map = WandererAppWeb.Factory.create_map()
+      system = WandererAppWeb.Factory.create_map_system(map.id)
+      signature = WandererAppWeb.Factory.create_map_system_signature(system.id)
+
+      %{system: system, signature: signature}
+    end
+
+    # The frontend reads these with `new Date`, which resolves a zone-less
+    # `2026/08/09 10:00:00` as *local* time. That silently shifted every
+    # signature by the viewer's UTC offset and pinned the scan-age bookmark at
+    # "0h" west of UTC. The zone marker is the whole contract: assert on it here
+    # so the format cannot regress to something ambiguous.
+    test "serialises timestamps as ISO-8601 with an explicit zone", %{system: system} do
+      [serialised] = MapSignaturesEventHandler.get_system_signatures(system.id)
+
+      assert {:ok, _dt, 0} = DateTime.from_iso8601(serialised.updated_at)
+      assert {:ok, _dt, 0} = DateTime.from_iso8601(serialised.inserted_at)
+      assert String.ends_with?(serialised.updated_at, "Z")
+      assert String.ends_with?(serialised.inserted_at, "Z")
+    end
+
+    test "the serialised instant matches the stored one", %{
+      system: system,
+      signature: signature
+    } do
+      [serialised] = MapSignaturesEventHandler.get_system_signatures(system.id)
+
+      {:ok, parsed, 0} = DateTime.from_iso8601(serialised.updated_at)
+
+      assert DateTime.compare(parsed, signature.updated_at) == :eq
+    end
+  end
+end