I voted 60 min, but it really depends on the c-bill income model. With each patch its been a little different. Ideally the last 20 minutes of the game should have a good deal of heavy/assault mechs. 45 minutes of assaults pounding on each other is a bit too long. Right now I feel it skips over lights and mediums and gets into heavies a little too quickly, so 45 minutes works well for 0.2.0, but 75 minutes was preferable for 0.1.1.