Depends if you're able to function on little sleep. I felt like I've done really well in my exams so far by waking up really early but I'm use to not sleeping a lot so it works for me. My schedule for today was;
4 - wake up and revise
8 - drive to college
9:30 - 3hr English Lit exam
12:30 - lunch (6 inch subway sandwich and 500ml can of monster)
13:30 - 2hr business exam
I didn't feel tired at all but that's due to me rarely drinking caffeine so I have a low tolerance plus I'm use to staying up for long periods of time. The morning revision is really useful and it stays fresh in your mind, I forget when I sleep. I wouldn't recommend doing it if you've never woken up that early before tho, it will **** you midway through the exam.