By your sig I am presuming you're in Year 11, and doing Biology 3/4 and Accounting 3/4?
Usually, in Year 11 I'd suggest that you dedicate a large proportion of your study towards your Unit 3/4 subjects. However, in saying that I don't encourage you to ignore your other units, especially Methods and English, you really want to nail the basics so that Year 12 does not become more difficult than it needs to be.
If you arrive home by 5pm I'd suggest that relax for a bit and grab a bite. Between that and dinner get your books out and sorted while lightly brushing over what you need to do for the evening.
I was in the same situation as you two Years ago (WOW so long ago), except I went to school in the country. Say if you start studying at 6:30, I'd split it into one hour blocks and at the end of that block give yourself a 10 minute break. So I'd say 3-4 hours of study a night is more than enough and is realistic.
I originally had a study schedule, but it's difficult to follow due to the reason you may get spontaneous assignments which need to be done first. For that exact reason I kept my schedule on a day-to-day basis, but make sure you're dedicated around 6-8 hours per subject per week, or whatever workouts for you.
The rules I followed from February-July:
-SAC study comes first
-Homework next
-Revision, e.g. checkpoint questions and sample exam questions.
Hope that helped