works for me :P I generally find just using the day before to cram the best option. You really can learn alot in a short amount of time, and if you understood it when you went through it in class, then it comes back to you almost straight away and all the pieces fit together, However, if you dont understand it at all, it takes alot of time. Take maths for example, after GCSE, I had to teach myself C1 and C2 using text books, it took a week or so.