I don't know how you approached the school certificate (lol school cert) but for most of our grade, we didn't really. I remember after school cert and year 10 we were all in the bludge-y mood. Come year 11 and a lot of people found it hard adjusting to the increased workload and different subjects. This has been mentioned a few times but you'll see a significant difference between the workload of junior maths and 3U prelim maths. You'll have to get used to doing homework daily to keep up with things.
But with that said, don't freak out too much. Use year 11 to really experiment with study techniques, figuring out what works best for you. Some people swear by study timetables while others are less disciplined but equally effective in studying, so it all depends on you really. In terms of the number of hours of study, I don't really remember doing solid hours of study after school, you'll find that homework generally takes up most of the time, and when you have hand-in tasks, you'll find that you don't really have "study" time, as funny as that sounds. Just keep on top of your work and you should be fine (for e.g i wrote notes every weekend rather than writing them up at the end of the term)
Basically, use year 11 as the experimental year, nothing counts towards your ATAR so don't get too worked up or stressed over anything yet. Most importantly, don't burn out. I worked pretty hard in year 11, and I found myself mentally exhausted when year 12 started, and even half way through term 2. So, just take it easy, and you'll be fine!