Best case scenario is, OP's still out there riding. He probably knows by now that riding 60+ miles the first day is quite possible, if one is in reasonable physical shape. Next morning, his joints, muscles and ass will be sore. Depending on how badly he wants to do it, he'll ride on, causing further physical discomfort that will take time to heal properly. He doesn't have that time, as he plans to do it in three days or less.
If he actually finishes in 3 days, odds are he'll hate cycling for the rest of his life. Best of luck in any case.
--J