I agree with JJF, for me there is such thing like overdoing, too. If there are courses at university, I train 4 - 5 times a week between 1.5 and 3 hours each, 3 times otherwise. I would prefer 3 times a week. It's not because I'm not fit enough. It's because I can not process what I've learned when I train too often. My progress seems not to be related to the amount of training I do. Sometimes my teacher has to stop me from training (at the moment, I'm highly motivated to get my shodan). So 2 - 3 times would be very fine, I think, at least for peaple who are like me.
Hope that helps,