I studied for 3.5 months leading up to last year's April test. The first two months, I studied an average of 4-5 hours/day. The last 1.5 months, I was freaked because I thought I was way behind, so I put in about 14-16 hours/day, no joke! It was an insane 6 weeks before the test. Oh yea, I went to my classes--occasionally.
I don't recommend studying for more than 8-10 hours/day. It's hard to retain anything beyond a certain point. I also got a bad case of insomnia, which was really really not helpful in the last few days before the MCAT. I became a madman, more or less...and now I'm back to normal, and sleep more than I should.