diff --git a/frontend/src/pages/pollView.tsx b/frontend/src/pages/pollView.tsx
index cf0bae8..0abd14e 100644
--- a/frontend/src/pages/pollView.tsx
+++ b/frontend/src/pages/pollView.tsx
@@ -74,6 +74,16 @@ function toLocalInput(value?: string): string {
   return new Date(date.getTime() - offsetMs).toISOString().slice(0, 16)
 }
 
+// The way back out. A zoneless "YYYY-MM-DDTHH:mm" reaching the API is read as
+// UTC, so a 9am start saved from Philadelphia comes back as 5am -- the browser
+// is the only side that knows which zone the editor typed in, so it has to say.
+function localInputToISO(value: string): string {
+  if (!value) return ""
+  const date = new Date(value)
+  if (Number.isNaN(date.getTime())) return ""
+  return date.toISOString()
+}
+
 function formatRunDate(value?: string): string {
   if (!value) return ""
   const date = new Date(value)
@@ -279,8 +289,8 @@ export default function PollView() {
           // "Now" and "scheduled" are the same published status; the start date
           // is what decides when readers see it.
           status: newTiming === "draft" ? "draft" : "active",
-          starts_at: newTiming === "schedule" ? newStartsAt : null,
-          ends_at: newTiming === "draft" ? null : newEndsAt || null,
+          starts_at: newTiming === "schedule" ? localInputToISO(newStartsAt) : null,
+          ends_at: newTiming === "draft" ? null : localInputToISO(newEndsAt) || null,
         }),
       },
       "Failed to create poll",
@@ -307,8 +317,8 @@ export default function PollView() {
         body: JSON.stringify({
           question,
           // Explicit null clears the date; omitting it would leave it unchanged.
-          starts_at: editStartsAt || null,
-          ends_at: editEndsAt || null,
+          starts_at: localInputToISO(editStartsAt) || null,
+          ends_at: localInputToISO(editEndsAt) || null,
         }),
       },
       "Failed to update poll",
diff --git a/server/internal/handlers/poll_handlers.go b/server/internal/handlers/poll_handlers.go
index 3dca439..51ec9e5 100644
--- a/server/internal/handlers/poll_handlers.go
+++ b/server/internal/handlers/poll_handlers.go
@@ -442,12 +442,12 @@ func PostPollRecord(conn *sql.DB) http.Handler {
 
 		startsAt, _, err := parsePollTime(body.StartsAt)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid starts_at")
+			writeError(w, http.StatusBadRequest, fmt.Sprintf("invalid starts_at: %v", err))
 			return
 		}
 		endsAt, _, err := parsePollTime(body.EndsAt)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid ends_at")
+			writeError(w, http.StatusBadRequest, fmt.Sprintf("invalid ends_at: %v", err))
 			return
 		}
 		if startsAt != nil && endsAt != nil && endsAt.Before(*startsAt) {
@@ -530,12 +530,12 @@ func PatchPollRecord(conn *sql.DB) http.Handler {
 
 		startsAt, clearStarts, err := parsePollTime(body.StartsAt)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid starts_at")
+			writeError(w, http.StatusBadRequest, fmt.Sprintf("invalid starts_at: %v", err))
 			return
 		}
 		endsAt, clearEnds, err := parsePollTime(body.EndsAt)
 		if err != nil {
-			writeError(w, http.StatusBadRequest, "invalid ends_at")
+			writeError(w, http.StatusBadRequest, fmt.Sprintf("invalid ends_at: %v", err))
 			return
 		}
 		// Only checkable when the same request supplies both; a PATCH that moves
@@ -837,6 +837,8 @@ func pollPageParams(r *http.Request) (int, int) {
 // unchanged; explicit null or "" (nil, true) means clear the column; a
 // timestamp (value, false) means set it. Collapsing null and absent would make
 // every PATCH silently wipe the dates it didn't mention.
+//
+// Timestamps must carry a UTC offset (RFC3339). See below for why.
 func parsePollTime(raw *string) (*time.Time, bool, error) {
 	if raw == nil {
 		return nil, false, nil
@@ -846,12 +848,17 @@ func parsePollTime(raw *string) (*time.Time, bool, error) {
 		return nil, true, nil
 	}
 
-	// datetime-local inputs submit "2006-01-02T15:04" with no zone, which is
-	// what the CMS poll form sends.
-	layouts := []string{time.RFC3339, "2006-01-02T15:04:05", "2006-01-02T15:04", "2006-01-02"}
-	for _, layout := range layouts {
-		if parsed, err := time.Parse(layout, trimmed); err == nil {
-			return &parsed, false, nil
+	if parsed, err := time.Parse(time.RFC3339, trimmed); err == nil {
+		return &parsed, false, nil
+	}
+
+	// A zoneless timestamp -- what <input type="datetime-local"> hands you
+	// unhelped -- used to parse as UTC, so a poll scheduled for 9am in
+	// Philadelphia went live at 5am. There is no zone the server can supply
+	// that is better than a guess, so make the caller state one.
+	for _, layout := range []string{"2006-01-02T15:04:05", "2006-01-02T15:04", "2006-01-02"} {
+		if _, err := time.Parse(layout, trimmed); err == nil {
+			return nil, false, fmt.Errorf("timestamp %q has no UTC offset; send RFC3339 (e.g. 2006-01-02T15:04:05-05:00)", trimmed)
 		}
 	}
 	return nil, false, fmt.Errorf("unrecognised timestamp: %q", trimmed)
diff --git a/server/internal/handlers/poll_handlers_test.go b/server/internal/handlers/poll_handlers_test.go
index 23c37f0..5d82160 100644
--- a/server/internal/handlers/poll_handlers_test.go
+++ b/server/internal/handlers/poll_handlers_test.go
@@ -67,3 +67,48 @@ func TestPollView_AlwaysCarriesState(t *testing.T) {
 		})
 	}
 }
+
+// A poll scheduled for 9am in Philadelphia once went live at 5am, because a
+// zoneless timestamp parsed as UTC. Silently guessing a zone is the bug, so
+// the parse has to fail instead.
+func TestParsePollTime(t *testing.T) {
+	ptr := func(s string) *string { return &s }
+
+	t.Run("absent leaves the column unchanged", func(t *testing.T) {
+		value, clear, err := parsePollTime(nil)
+		if value != nil || clear || err != nil {
+			t.Fatalf("got (%v, %v, %v), want (nil, false, nil)", value, clear, err)
+		}
+	})
+
+	t.Run("empty clears the column", func(t *testing.T) {
+		value, clear, err := parsePollTime(ptr("  "))
+		if value != nil || !clear || err != nil {
+			t.Fatalf("got (%v, %v, %v), want (nil, true, nil)", value, clear, err)
+		}
+	})
+
+	t.Run("offset is preserved as the instant it names", func(t *testing.T) {
+		value, clear, err := parsePollTime(ptr("2026-08-07T09:00:00-04:00"))
+		if err != nil || clear || value == nil {
+			t.Fatalf("got (%v, %v, %v), want a parsed time", value, clear, err)
+		}
+		if want := time.Date(2026, 8, 7, 13, 0, 0, 0, time.UTC); !value.Equal(want) {
+			t.Fatalf("parsed %s, want %s", value.UTC(), want)
+		}
+	})
+
+	for _, raw := range []string{"2026-08-07T09:00", "2026-08-07T09:00:00", "2026-08-07"} {
+		t.Run("zoneless "+raw+" is rejected", func(t *testing.T) {
+			if _, _, err := parsePollTime(ptr(raw)); err == nil {
+				t.Fatalf("parsePollTime(%q) succeeded; a zoneless timestamp must not be assumed UTC", raw)
+			}
+		})
+	}
+
+	t.Run("nonsense is rejected", func(t *testing.T) {
+		if _, _, err := parsePollTime(ptr("next tuesday")); err == nil {
+			t.Fatal("parsePollTime accepted a non-timestamp")
+		}
+	})
+}
diff --git a/server/internal/models/api_responses.go b/server/internal/models/api_responses.go
index 5b5ddd7..75b0b82 100644
--- a/server/internal/models/api_responses.go
+++ b/server/internal/models/api_responses.go
@@ -450,6 +450,10 @@ type PollResponse struct {
 // PollRequest creates or updates a poll. Pointer fields distinguish "not
 // supplied" from "set to empty", which is how a PATCH clears an end date
 // (explicit null) without every other PATCH wiping it.
+//
+// StartsAt/EndsAt must be RFC3339 with a UTC offset. A zoneless timestamp is
+// rejected rather than assumed to be UTC, which used to move a scheduled poll
+// by the paper's offset.
 type PollRequest struct {
 	Question *string  `json:"question"`
 	Status   *string  `json:"status"`