Actually, I was reading some entries in the devlogs about fat layers in the new organ and tissue composition system for creatures. If you burn fat as you walk and do tasks, you eventually have to replenish with more food. Your total stamina would represent the rate at which you burn, with a higher attribute representing slower fat burning. However, to offset this, the higher your strength or your agility, the bigger tasks you can complete at a faster rate. I know Toady has aims in mind for updating dwarf attributes, but I'm pretty sure some analog of those will remain.
Now, here's something interesting: the dwarves should have to poop for every meal they eat. The more you eat, the more you have to poop. The more you drink, the more you have to pee. Have these two tied in with some form of hunger and dehydration system for the dwarf metabolism.
Hell, you could enough tie fatigue into some formula of physical attributes, and that would determine when dwarves have to sleep. You could have some period of being tired where they begin to perform their tasks slower until they eventually go somewhere to fall asleep. You have a low water mark for when they begin to feel tired, a medium watermark for when they begin to get anxious to seek out a place to rest if they're not in mortal danger, and then a high watermark for when they could pass out at any second even in the heat of a pitched battle. Then, whenever any dwarves are over the high watermark threshold, there's a random probably of them falling asleep on the spot.
All of these consume, store, utilize, begin to run out, dangerous low resources left, emergency state cycles would just entirely make a semi-closed system of production vs. consumption of food and waste and hygeine and tiredness creating an entirely different cycle of dwarven behaviors and interactions.
Later on, if there are proper day/night cycles in the game, you could set hours for certain groups or squads or burrows. It would be an interesting balancing act of keeping your dwarves healthy and happy with enough sleep and food and bathrooms and tasks, and not having your fortress descend into a tireless march of haggard and weathered dwarves just barely surviving in the wilderness.
This could also most certainly be an interesting ballet to watch during seiges...