diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 2d35076..2d185c3 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -877,10 +877,26 @@ public sealed class GameWindow : IDisposable
             _loadedSkyDesc = AcDream.Core.World.SkyDescLoader.LoadFromRegion(region);
             if (_loadedSkyDesc is not null)
             {
-                WorldTime.TickSize = _loadedSkyDesc.TickSize > 0 ? _loadedSkyDesc.TickSize : 1.0;
+                // Phase 3d: do NOT assign WorldTime.TickSize from
+                // SkyDesc.TickSize. Agent C's decompile (chunk_00500000.c:6241
+                // FUN_005062e0) shows SkyDesc.TickSize is the "next sky-tick
+                // deadline" period — a throttle — NOT a game-time
+                // advancement rate. ACE's server advances PortalYearTicks at
+                // 1.0 ticks per real-second (Timers.cs: `PortalYearTicks +=
+                // worldTickTimer.Elapsed.TotalSeconds`). Our client
+                // extrapolation between TimeSyncs must match: 1.0.
+                //
+                // Previous behavior: WorldTime.TickSize = 0.8 (from the live
+                // SkyDesc.TickSize). Between ~20s TimeSync gaps we fell 4
+                // ticks behind the server, producing a visible "acdream sky
+                // is behind retail" time-of-day mismatch (user-verified
+                // 2026-04-23).
+                WorldTime.TickSize = 1.0;
+
                 Console.WriteLine(
                     $"sky: loaded Region 0x13000000 — {_loadedSkyDesc.DayGroups.Count} day groups, " +
-                    $"TickSize={_loadedSkyDesc.TickSize}, LightTickSize={_loadedSkyDesc.LightTickSize}");
+                    $"SkyDesc.TickSize={_loadedSkyDesc.TickSize} (throttle, not rate), " +
+                    $"LightTickSize={_loadedSkyDesc.LightTickSize}");
 
                 // Initial DayGroup roll using whatever WorldTime currently
                 // has (either the hardcoded boot seed or a pre-arrived