In the kingdom’s health regulation for the army, the obligatory sleeping time during a campaign is reduced to six hours once per day at the lowest for soldiers.
Erw’s group has only half of that sleeping time.
“Elise-jou-chan, isn’t there also a spell to reduce fatigue within healing magic?” (Burkhart)
If you use ‘Reduce Fatigue’, a person will be able to continue battling for about a whole day.
But there is no effect on the mental weariness. It becomes impossible to move for several hours on the next day in the end.