I often won't study till the morning of the exams (yep, not even the night before). I still kicked arse at the HSC last year. If you want to do well, I'd merely suggest doing shitloads of past papers. Even I did a few of those.
But man, 3 hours a night, 7 on a weekend! You're gonna burn yourself out or discover you've neglected friends and family at the end of the year. If your gonna study a lot, either do it during the week and leave your weekends free, or vice versa. You need rest time.