How long should i revise for?

Im doing important exams the first of which is in 2 1/2 weeks however i havent started revising yet :S I know its really stupid but I just cant seem to be motivated. I was wondering how long I should revise for from now on because its SO important and I really want to do well. I think im just so nervous that I cant face revising and not knowing the answers. I really want to get into uni but need great grades but somehow this hasnt translated into lots of work. Its so stupid of me and I recognise this and yet...I dont revise. Anyways, how long would you say I should be revising per day for my highers? Highers are scottish qualifications, they are taken over a year and are the equivalent of 2/3 of an A level. Im doing 5 highers and its just so daunting cos theres so much work to do. Well anyways sorry for rambling but van anyone motivate me? Yell at me even?