Play crunch time when you MUST win the game, against an opponent that is beatable by your team, but a tougher game for you. Crunch time will use all your enthusiasm, meaning your teams next few games, they wont play as well as they should, as your enthusiasm is low. To build enthusiasm, play TIE. Get your enthusiasm up to 11-12 and youll be performing much better as a team.
I wouldnt use crunch time until finals, when its do or die. Even then you need to save enthusiasm, but that a different tactic...