Relax, you have plenty of time. I'd suggest starting whenever the Easter holidays officially begin for you; start with maybe a couple of hours a day and then gradually build up. There's no magic number or hard and fast rule as to how long you have to be sufficiently prepared for your exams - it differs completely from person to person. Ensure the revision you are doing is effective and don't be afraid to take a break or have a day off every now and again.
Best of luck. Panicking like this isn't going to help you in the slightest.