People R putting question differently want sleep,anyway If Your subconscious mind well aware about your study plan exams dates your need to clear the Exams is of utmost Importance on account of your social financial and family commitment you will wake up without putting alarm at the early hrs of morning as You wish.
Sleep is the process of your body and mind system getting relaxation to function effectively further.
Things which are done with immense interest and enthusiasm would not allow the mind and body to get tired soon.Therefore , motivate very highly yourself and involve your mind in studies with immense interest. You will surprisingly find that your body will accomodate your study programmes without any external help.
try this (I also tried in Final):
Always sleep straight and without a pillow during xam preparation days for at least 5-6 hrs. (First 2-3 days may be problem but then you will get results)