I just did a very quick Test using the Beda Fomm map.
An Italian Infantry Coy, 9 Compagnia, III Btg 86 Reggimento, travelled 43 Km starting off at 30% fatigue, with No Rest set for its orders primarily over open terrain, with a 67% foot movement modifier.
It travelled through the night in light rain.
It gave out at 88% fatigue where it was forced into rest in situ.
The fitness stat for the unit was 38%, which is quite low.
I have to goto work now, so will see how long it takes to recover when I get back.
Nice one. Can't wait to get to know how much time they will need to recover (and how much time it will take to "convince" them to start their 2nd day of force marching).