How many hours a week should I be revising to ace my GCSEs?

I am targeted A*s in all of my subjects(apart from RS) and I want to start revising to make sure i meet as many of my targets as I can. I want a guide to how many hours I should be putting in each week so I can set up a revision timetable. My exams are in order of the date with the first being on the 13/05/14 and the last being on the 13/06/14:

Biology Unit 3
Geography Unit 1
ICT Unit 1
Law Unit 1
Physics Unit 3
Law Unit 2
Chemistry Unit 3
English Literature Unit 1H
Religious Studies Unit 2
Geography Unit 2
English Literature Unit 2H
English Language Unit 1
Religious Studies Unit 7
Maths:Additional Mathematics (Not a GCSE this one, extra qualification in which you get UCAS point for I believe)
Mathematics A Paper 1
Mathematics A Paper 2

Thanks for your help

some people will tell you none. how these people aced their exams with no revision is a miracle..

try to do as much as you can, but do not overwork yourself, make sure you eat, do something you enjoy and sleep at a time where you will not be tired the following morning...

do between 2-4 hrs each day, perhaps leaving the weekend off or doing a bit less.. but never start revision too late, do it maybe between 5pm and 9pm. always take breaks periodically..

just remember its not for how long you revise for, its how you revise which will be more effective, dont just sit there and read books and hope something goes in, this is only good for cramming for the evening before the exam..