umm...pre year 12 it was always start studying the night before.
nowadays....i think i started 3 weeks pre-half yearlies...and about 3-4 weeks pre-trials too. unfortunately its not been enough time even though i have 2 weeks left...i feel i should have started earlier.
i heard that you should aim to finish all your subject notes 3-4 weeks before the trials. and when you write your notes, you should spend 1/2 hour revising what u just wrote/typed. Then just practise past papers.