I believe it changes for everyone. If you have that brain capacity, the intelligence, you wont need to study as long as other people.
For example, last years from my school, I surveyed two of the top scorers. One scored 97.5, one 99.35.
The boy who achieved the 99.35 result said that he did around 4 hours of study a day and possibly around 6 on weekends.
The guy who got 97.5, you wont believe it, studied around 6-7 hours a day. And even longer on weekends.
I think he really 'drained' it though.
Too much is not good, too little would do no good.
And to be honest, even though I don't have complete experience, taking weekends and friday's off would just ruin your VCE studies and eventually your Atar score.
I take friday's off though. Everyone needs a day to relax and refresh their minds.