I have been practicing 3 hours a day for about a month now. I break it up into hour long sessions and this routine seems to allow for quite a bit of weekly improvement without causing extreme tiredness or strain on my hands.
I whole heartedly agree with what has been said about a difference between just playing and actually practicing. Just running through a piece before you have it completely under your fingers will not help you learn it as fast as breaking up a piece into sections and really drilling the difficult parts until they feel natural.
-Pete
