Modern Campaigns: noob query re. turn delta

[neonlicht]

Re. the Modern Campaigns series (Fulda Gap, Danube etc.): is there any major reason why day turns last 3 hours and night turns 6 hours? Not a big deal---but was just curious if there was some special importance to these values? For example, why not 1-hour turns for both day and night? The game scale is 1-mile per hex and units not in travel move usually move 1 hex per turn (i.e. 1 mile in 6 hours at night).