If I remember right, Fury in the West had a fantastic way of dealing with the length of the day and exhaustion. Each unit (Brigade, I think) had a Strength Point track. Casualties would move from one end while every hex/few hexes (can't recall which) you moved, you'd move another point tracker from the other side of the track. This way if you moved a unit too much, they'd lose a lot of stragglers; but if you kept it in place after it had moved a lot, it would regain some of them. I think day lengths were variable too, and the game (which depicts the Battle of Shiloh) is played over two days. The first day, the Rebels had the Northerners on the run, but got too weak to press their advantage; the next day, Grant appeared with reinforcements at Pittsburgh Landing, and that was the end of the Rebel attack.