I agree that military dwarves should be a bit more punctual, since being in the military is a duty, not a simple job. Wandering off for a break or naptime in the middle of a siege is going AWOL, and going AWOL during a battle is delt with quite harshly.
A possibly easy way to do this could be that during sieges, all military dwarves ignore their basic needs unless they're about to die of hunger or thirst. But just having the munchies or wanting naptime because you yawned? Not a value excuse!
By linking this to siege mode, the military would automatically head to their stations without the player needing to micromanage, and by having it so they will still take care of basic needs but only if the situation is dire, dwarves don't be killing themselves for no good reason during a prolonged siege.
One other thing I'd like to see would be better squads. Right now if the squad leader wanders off for naptime, he'll drag along his 20 subordinates to bed with him.
...which is probably why female military dwarves are so dang fertile...
If the leader dwarf has to leave his station for some reason, a second in command should automatically take over and anchor the squad. And so on and so forth down the chain of command. Alternatively, remove the link between subordinate dwarves and the leader, instead having a "phantom dwarf" be the leader. Really just a marker. It'd function like a regular military dwarf squad leader, except it cannot be harmed, cannot attack, doesn't eat, sleep, or drink and is only spawned or despawned when the squad is assigned to a particular location. Basically just something to keep the squad in place.