What's the best way to not procrastinate over such long exams?

I'm 15, and I have this incredibly long series of exams. Three hours of writing, three hours of listening, three hours of speaking, and most of the exams are at 8 in the morning. I tend to burn out really easily in general, but I'm especially stressed out with these exams. I just have a hard time with long exams, especially when they're at 8 in the morning. I'm so drained right now. What should I do to not procrastinate and study effectively?