I did 12 hours a day from march onwards, but I had double the amount of exams... I also know people who do zero revision and end up with full marks, and others who do maybe 3 hours a day in exam period after doing little bits throughout the year. Make sure whatever you do, you are happy with it.
Maybe you could try doing something like a revision timetable? I did this and it helps you plan what topic you will do each day. Make sure to keep the topics varied so you don't get bored, and give yourself strict breaks (50 mins revision, 10-15 minute break where you leave your desk, down some water, get some fresh air, lunch, dinner and time to relax before bed). Otherwise you won't be productive and will burn out. I gave myself a week or two before exams to then just calmly read things to jog my memory. If you do that amount of revision make sure you are strict with yourself and take a 10 minute break away from your desk every hour (maybe go outside) and take some time off at lunch and dinner, and before you sleep so your mind is rested.