It would be awsome if the game engine could simulate night battles, but the only way that it would do it is if your in a battle during the day and it goes into the evening. I know that back then they did not fight a whole bunch but there are cases that they did like Hood at Second Manassas
then other battles out in the west they had some battles that continued into the night, Also the battle of Chancellorsville continued into the night. Night battles could be mostly just skirmishing because usualy they ended up in confusion. It be interesting if it was possible for the engine to do this, but if it can not it doese not matter cause this game is still the best.