Please note you are being very ambitous in your 21 hour time limit for 65 miles that would be a good time for professional soldiers, The average walking speed is somewhat less than 3mph and that is over short distances it tends to drop the further you are walking, With allowing for comfort breaks etc and food input you would usually be looking at an average speed of 2 to 2.5mph still a good speed, 3mph is pushing it quite a lot one person in 20 might make it because even average Marathon runners take four and a half hours to RUN 26 miles. I wish you luck with your endevours however I know what it is like having regularly walked between Harringay North London(where I lived) and Reading (Where my girlfriend lived) many times when I was younger, fitter and unemployed.
