A shame - the time limit pretty much ruins campaign play for me, but I'll still have the single battles to enjoy and there's more than a few of them so I'll live.
I hope, though, that you will make it possible to continue a battle after the time limit expires at some point in the future, or solve this issue in some other way, so we dont have to miss the climax of a battle.
Punish the player in the final score for not keeping to the schedule, but don't ruin his gaming experience by kicking him out of the game. That's just mean... ;-)