Well, I just registered for the noon exam... and for me, I don't really wake up until around 11 anyway. What time do you wake up? Maybe sleep in a little!
But seriously though, I don't think it'll be a huge deal. Just keep practicing, and you'll build plenty of stamina for whenever you want to take it. Maybe do some errands and other stuff before noon if you're an early bird, and then focus on MCAT for the rest of the day.
I'm gonna' do BK review until the end of december, then do Kaplan topicals/PS/BS tests staring January till February, all the while doing EK verbal 101, and begin taking 2-3 full lengths a week until between Feb. and test day!
I'm sooooo glad I changed my date from Jan. 31st to March 28th! I'd be overwhelmed otherwise!