Note that there are no headlights either - you can drive your 200MPH supercar at full blast lights out down a windy forest dirt track with no problems in the pitch dark in the SP universe, it has some weird physics
Edit to add - and you can hang a 90 degree turn at 200MPH, suddenly come across Farmer Giles on his pony and trap and stop without turning them into pate as well...
For those who have to rationalise, maybe just think of a daylight turn as 5 "administrative minutes" rather than a minute or so (to allow for real life units not all moving in synch, all the hurry up and wait amd "4 Alpha, this is 3 bravo, say again all after.. ".
And any night move (vis under 10) - count that as say 15 administrative minutes to add to your campaign time clock.
After all - I could programme in a 50% move deduction for visibility less than 500 yards, but most players would say "to heck with all that" and edit the start map selection to vision >10 and never play "night rules" battles (most probably already avoid such anyway I'll bet).