It's basically a fundraiser. You just ride as much as you want, with no distance goal unless you set one for yourself. I think it would be way easier to ride 100 miles in 24 hours than in 10 hours. Take a break every hour, take a few hours off in the middle of the night to sleep...
But being a morning person, starting at 4 in the afternoon would not be fun.
PedalWench, that sounds like a grueling schedule of driving and riding. I couldn't do it, but more power to you!