The only difference being in shape makes is how long it takes you.
Yes, but not much difference in time. An in shape rider will put in big miles the first month. An out of shape rider will put in small miles the first month. Maybe 30 miles per day difference for the first couple weeks. After a month both riders are in equal tip top fit shape and can ride the same mileage. So in the first month the fit rider gains an extra 5-600 miles on the out of shape rider. It takes an extra week for the out of shape rider to finish. An extra week over an entire summer. Not much difference. 13 weeks instead of 12 weeks.