hey chill with the time table!
I personally would not stress myself by dividing my day so strictly...
I bludged so much during year 12 that i seriously doubt it is necessary to have a full study plan unless you are gunning for like 99.95.
just remember a few simple rules:
1. Maths should be done as regularly as possible (aim to do maths basically every day - hw should take at least an hour every night and this should be sufficient for 2 unit maths) as it requires constant repetition.
2. English, the best thing to do is simply start very early with your practise essays so you can get it fixed by your teacher many times. Also, simply consider about what you want to write about throughout the day (on the bus, walking home, eating dinner) that way you don't waste time just sitting there at your computer blanking out. it works wonders trust me
3. modern history just write your notes for syllabus as your teacher goes through it at school... be on top of this as it can get overwhelming during hsc time if you don't write your own notes at the start of the year. (because alot of content). it doesn't take long to write notes so 3 hours a week on writing notes for modern history would be the maximum amount of time you would ever ever ever need to do. (i personally didn't write notes for mod history and hated myself come hsc time bcuz i just had 2 boxes of textbooks and printed texts from teacher).
4. biology - like all sciences, you should write your notes for it as soon as possible (even ahead of your teacher) then simply revise it as your teacher covers it in class. by test time you will know everything back to front. (Just spend 2 hours writing notes every now and then to keep ahead of the class).
5. try to do maximum 2 subjects in one night... better to go in depth in two subjects than shallow in 3.
iuno about ext history or legal tho...
Anyways, I assure you 2-3 hours every night is MORE than enough to secure you a pleasing result. You could skip many nights of work totally and still make up for it in a few days, so don't stress!
gl hf with the hsc