You guys honestly don't need to be doing 4+ hours of study a night. I did all my homework and assignments (which with my subject workload varied each week, but was anywhere between 1 hour and maximum 3 hours a night.) I would only do reading over notes of the week on the weekends, and then do some extra reading during the week for case studies in legal, source analysis in Ancient / Modern, novel reading for English. The only time I had set hours of study was just prior to exam weeks / assessment weeks, and then it'd be only a couple of hours a night (if that).
Don't stress too much guys. Trust me, you don't need to focus on how many hours you do a day, but more so what you now understand better or have learned due to your study. (You might understand something better in 10 minutes, rather than spending copious hours re-reading the same information). Don't burn yourselves out, and the best of the luck with Preliminary. n_n Enjoy your year guys, and remember work on establishing the necessary study habits that are needed for year 12, learn how you work best; not how others do.