Me too. I feel similarly.. did I make a mistake taking the later slot? I might be really glad of the extra sleep the night before. The 400 I did started at 9am and it was great to start an audax without the first 3 hours trying to warm up and get my body started. Time will tell, I suppose.
I'm also doing this one. Kind of annoyed I went with the 7.30 start now as would prefer to spend less time in the dark.