Hi Zoe!
I'm not out of the woods of year 12 yet (dang), but my older sister got a 95 ATAR, and she followed the same schedule as I am:
About 4 to 6 hours of study a night, depending on the amount of work needed to be done / study you're comfortable with (this includes short food/coffee breaks haha). I get home at 4, rest until maybe 4:30, then get stuck into it. I take about an hour-long break between dinner and my later studying. Getting at least 8 hours of sleep is vital, so I go to bed at 10:30 and wake up at 6:30, although I'm not very good at going to sleep on time, nor waking up on time, especially on the weekends!

I work two nights a week, so I leave time for that (5 hours), and I give myself the mornings on the weekends to just relax if I'm not stressed for time, because I suck at studying in the mornings. Follow your own peaks and lows, find the best time for you to study.
Just a side-note, it's important to socialize as well. Plan your meetings and study steadily, but don't burn yourself out studying more than you're comfortable with. Hold a schedule you feel is right for you, and don't feel guilty if you need a break. We're humans, we need rest!
Good luck!

Poet