The Eastern PA 400k has always started at 4am and I think I have seen more second sunrises than the number of times I have finished in the dark. The first time that happened was when I was sick all spring and the only training I got was riding brevets. But usually it's because it's relatively early in the year and I have trouble eating. That's what happened this year. One time it was because my knee blew up and I rode the last 20 miles pedaling with one leg because I couldn't stand to flex the other leg anymore. That will slow you down, but the saddle sores are epic. I was really happy last year when I finished the 400k with a decent time.