Alright,
During my HSC, I did the 9am-9pm thing at State Library - started about 3 weeks before English exam 1, and was there everyday until night before my last exam. Firstly, u obviously dont spend 12 goddamn hours a day studying, it's just that u are there for 12 hours, but u take regular breaks, ie half hour in the morning, an hour for lunch/walk/galaxy world, and another hour mayb in the late arvo. It worked pretty well because u'd get about 9 or 10 solid hours of studying done, and u dont feel tired or anything at all because u take regular breaks.
Even if u haven't been trying that hard all year, u can make so much difference by putting in extra effort now. Seriously, with my assessments/ranks, I was looking down the barrel of a UAI in the 80's, but I wanted to do Commerce/Eco's so badly that I forced myself to the library for that long, and I ended up with a UAI of 95.25. What's done isnt done yet