Seriously some of you guys need to RELAX - especially those working towards GCSE examinations. Doing over 4 hours a day (and even then that's a bit much) when the exams are still so far away is not as effective as you might think - you will burn out a week or two before the exams and not be at your best when you really need to be. It happened to me with my first exams.
At A-Level it really depends on what subjects you took and how much you worked throughout the year but I can honestly say I never worked much more than 4 hours a day, and that was really just the 3 weeks leading up to the exams.
You can take or leave what I say - I'm not one of those people who says 'You don't have to work at all and you will still do fine' or 'GCSE's are EZ MODE!!' but I think some of the mentality on here is quite sad at a time in your lives where you really should enjoy yourselves. I got 5 A*'s and the rest A's at GCSE and A*A*AA at A Level so, while trying to retain some modesty, I think there is definitely some merit in what I say.