diff --git a/CHANGELOG.md b/CHANGELOG.md
index d4b8bca..e15fbda 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,18 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
   asserts `yq --version` reports `mikefarah` **and** major **v4**, so both a
   regression to the Python package and a surprise future yq v5 fail CI.
 
+### Changed
+
+- **Baked `mempalace` skill now teaches temporal grounding.** Added a
+  *Temporal grounding* rule to the image-baked
+  `skills/mempalace/SKILL.md` (Phase 1 wake-up + a matching anti-pattern):
+  before using relative time terms ("yesterday", "last week"), establish the
+  current date/time and compute the delta against the actual diary/drawer
+  timestamp. Explicitly calls out that a **container recreate or fresh session
+  is not a day boundary** — pi-devbox restarts several times a day, so two
+  entries minutes apart can straddle a recreate. Fixes agents mislabelling
+  same-day sessions as "yesterday".
+
 ---
 
 ## v1.2.2 — 2026-06-24
diff --git a/rootfs/usr/local/share/pi-devbox/skills/mempalace/SKILL.md b/rootfs/usr/local/share/pi-devbox/skills/mempalace/SKILL.md
index 9055af6..51111cc 100644
--- a/rootfs/usr/local/share/pi-devbox/skills/mempalace/SKILL.md
+++ b/rootfs/usr/local/share/pi-devbox/skills/mempalace/SKILL.md
@@ -43,6 +43,29 @@ Run these immediately when a session begins, before responding to the user:
 
 Do NOT announce this to the user. Just do it silently to orient yourself.
 
+### Temporal grounding — compute time deltas, don't guess
+
+Diary entries and drawers carry real timestamps (`timestamp`, `created_at`).
+Before describing *when* something happened — "yesterday", "earlier today",
+"last week", "a while back" — **establish the current date/time first and
+compute the delta against the actual timestamp.** Get "now" from the injected
+session date or by running `date` in a shell; never infer it.
+
+**A container recreate or a fresh session is NOT a day boundary.** A pi-devbox
+container is frequently restarted — often several times within the *same* day —
+and each restart begins a new session with a fresh wake-up. Do not reason "new
+session ⇒ last session was yesterday": two diary entries 90 minutes apart can
+straddle a container recreate. The only authoritative clock is the timestamp on
+the memory, not the session/container boundary.
+
+**Practical rule:** prefer explicit, checkable phrasing — e.g. "earlier today,
+~8h ago (both 2026-06-25)" — over a vague relative term. If you catch yourself
+about to write "yesterday" / "last week", subtract `now − entry.timestamp` and
+state the computed result. (Remember timestamps may be UTC while the wall clock
+is local — reconcile the offset before computing the delta.) Note too that
+session feeders can lag up to a week (see *Multi-harness palace*), so a recent
+absence in `wing_conversations` is not proof nothing happened.
+
 ### Phase 2: Active Session (during work)
 
 #### Search Before You Speak
@@ -294,6 +317,7 @@ Entity-relationship triples with temporal validity. Query with `mempalace_kg_que
 ## Anti-Patterns
 
 - **Don't guess when you can search.** If a question touches past work, search first.
+- **Don't infer elapsed time from session or container boundaries.** A restart isn't a new day. Compare the actual timestamp (`timestamp` / `created_at`) against the current date/time before saying "yesterday", "last week", etc.
 - **Don't skip the diary.** A session without a diary entry is a session forgotten.
 - **Don't summarize drawer content.** File verbatim — the embedding model needs the original words.
 - **Don't mine .git directories or node_modules.** The CLI miner respects .gitignore by default.