Self-study is one of the most important things to do in order to qualify for an examination. Number of hours does not actually come into play when you can actually study for 2 hours with the efficiency of 4 hours slog and there's no point in studying more.
In classroom teaching, there are several factors which actually hinder the outcome of good learning. Since, the syllabus is quite huge and teachers are burdened to complete the syllabus in a restricted time frame, they often go on a faster pace. Pace doesn't affect one's learning process as much as the duration of each class. Long classes actually saturate students and they often feel tired and become less receptive. And in such a situation, you can't even take a break and let your brain become receptive again.
That's where self-study outperforms the classroom teaching. When you are studying by yourself you can actually take some time off and take break in order to get back to your usual self as an average student gets tired in an hour or an hour and a half.
All you need to do is to, draft a schedule and start working towards your goal in a systematic method. Do not add up sky high study hours in your schedule as you are bound to lose on the track. Keep it straight forward and allot time to your subjects equally.
I am going to tell you something interesting about the toppers in the IIT JEE 2008 examination which I got to know from one of my friends. The first ranker used to study for more than 15 hours a day whereas the second ranker just studied for 5-6 hours. Isn't this astonishing? By now, you should have understood that number of hours is not important but qualitative study is very important.
If you haven't started doing this, start now as preparation which begins early will yield a much better result.