It's not all about the amount of time you spend, it's more importantly what you spend it on. E.g spending an hour per day rereading the math textbook is so ineffective that it may as well be counterproductive.
To be an efficient AND effective band 6 math student I'd suggest:
1) Focusing on past papers (after having learnt the content) and CHECKING and LEARNING from your mistakes.
2) Prioritise your weakest areas. Focusing on the areas you're already good at may feel good now, but your weakest areas will absolutely slam you out of the B6 range in the HSC.
3) Be consistent but space specific topics out. Spending 8 hours straight on revising one math topic is nothing compared to the benefits of spreading that over a week, month and term (see the forgetting curve).