diff --git a/UAT_PLAYBOOK.md b/UAT_PLAYBOOK.md
index 1e3a021..c1452e9 100644
--- a/UAT_PLAYBOOK.md
+++ b/UAT_PLAYBOOK.md
@@ -237,6 +237,24 @@ export const { signIn, signOut, useSession, changePassword } = authClient;
 > absolute `startTime` in `isUpcoming`, and hardens `parseTimeTo24Hour` against
 > blank/undefined input.
 
+#### 5.12e Book New `preferredTime` Formatting (GRO-2211, GRO-2213)
+
+| # | Scenario | Steps | Expected |
+|---|----------|-------|----------|
+| TC-WEB-5.12.22 | Slot buttons show formatted label | Sign in as `uat-customer@groombook.dev`, open `Appointments`, click "Book New", select a pet and service, pick a date with availability | Each time-slot button shows a human-readable label like `10:00 AM` (UTC), never a raw ISO timestamp (e.g. not `2026-06-09T10:00:00.000Z`) |
+| TC-WEB-5.12.23 | Confirmation review shows formatted label | Continue the Book New wizard to the Review step | The "Date & Time" summary and the final confirmation both display the formatted slot label (e.g. `10:00 AM`), not a raw ISO string |
+| TC-WEB-5.12.24 | Booking submit succeeds (regression) | Complete the Book New wizard and submit the request | Request succeeds with no `500` / `invalid input syntax for type time` error; the booking POST sends `preferredTime` as `HH:MM:SS` (e.g. `10:00:00`); the new appointment appears in the Upcoming list |
+
+> **GRO-2211/GRO-2213 note:** The Book New wizard previously rendered the raw
+> UTC ISO slot string as the button/confirmation label and submitted that same
+> ISO value as `preferredTime`, which the API rejected with
+> `invalid input syntax for type time` (HTTP 500). The fix adds shared UTC
+> helpers `formatSlotLabel(slot)` (display → `10:00 AM`) and `slotToTime(slot)`
+> (payload → `HH:MM:SS`) in `src/portal/sections/Appointments.tsx`, so the
+> displayed label and the submitted `preferredTime` both derive from the same
+> canonical UTC ISO slot. (The sibling `RescheduleFlow` `startTime` raw-ISO issue
+> on a different endpoint is tracked separately and is out of scope here.)
+
 ### 5.13 Reports UI
 
 | # | Scenario | Steps | Expected |