[narwan]

A time limit does NOT make it more realistic. The usual reasoning for it goes something like "a real force commander has a limited amount of time to make decisions so why should a player have all the time he needs?" The answer is very simple, in reality every single commander in the force (so including every specific unit commander) and many of the other individuals in those units will add their 'brainwork' to the decisionmaking process and they'll be doing that all at the same time (i.e. during a turn).
As a player you're in effect playing every unit commander, not just the overall commander. So the available time should be close to the total amount available to all those unit commanders and that would be hours per turn.

Narwan