Clarify MVP time pacing

Docs/MvpSurvivalReadinessCriteria.md

@@ -5,30 +5,36 @@ success, failure, and closed-test readiness.
 
 ## Day And Night
 
-MVP rule: day/night should mimic the real Earth region represented by the
-loaded map tile.
+MVP rule: day/night presentation should mimic the real Earth region represented
+by the loaded map tile, while the gameplay calendar uses the MVP pacing target
+of `4 real hours = 1 in-game day`.
 
-For Ground Zero, the server-authoritative world clock should follow the local
-time of the real Ground Zero region. Weather and sunlight should both come from
-the same real-world tile context so the player feels like they are standing in
-that place, not in an abstract accelerated map.
+For Ground Zero, weather and sunlight should come from the same real-world tile
+context so the player feels like they are standing in that place. The sky should
+respect the region's local time zone, sunrise/sunset shape, season, and weather
+direction as the system matures, but the MVP gameplay day is still compressed
+to four real hours so players can experience a full survival cycle in a
+reasonable test session.
 
 Implementation target:
 
 - The server owns time and replicates it to clients.
-- Ground Zero uses the real local time zone for its real-world coordinates.
+- The MVP gameplay calendar target is `4 real hours = 1 in-game day`.
+- Ground Zero day/night presentation uses the real local time zone and regional
+  solar/weather context for its real-world coordinates.
 - Sunrise, sunset, day length, night length, and seasonal light should be based
   on the tile location as the system matures.
-- The MVP fallback can use a 24-hour local clock with conservative fixed night
-  bounds until real sunrise/sunset lookup is implemented.
-- Time acceleration is allowed for test commands and automation, but not as the
-  default player-facing world clock.
+- The MVP fallback can use the accelerated 24-hour gameplay clock with
+  conservative fixed night bounds until real sunrise/sunset lookup is
+  implemented.
+- Additional time acceleration is allowed for test commands and automation, but
+  should not replace the default four-hour MVP day for normal playtests.
 
 Design consequence:
 
-- The sky clock stays grounded.
+- The sky stays regionally grounded even while the gameplay day is compressed.
 - Skills, tools, teamwork, shelter, storage, domestication, and infrastructure
-  improve what players can accomplish inside real time.
+  improve what players can accomplish inside the compressed gameplay calendar.
 - Natural biological systems should not be casually compressed just to make
   progress feel faster.