Go with whatever you're best mentally fit schedule is. Personally, I feel brain dead at 8AM, even if I maintain good sleeping habits and get up at 6AM let's say for work. People throughout my life have commented I look miserable at that time of day, but once it hits 11 or 12 I have a ton of energy while everyone else is burning out, so go figure.
My sleep schedule was terrible this summer, so 2PM worked out best for me. The 2PM exam was actually great, got up at 10, cooked a power breakfast, relaxed a bit, ate lunch on the way to the exam, and the test center let me start at 1:30 anyway so I was out in time to have a good dinner and enjoy the night.