10 miles x 10 days in a row?
That sounds crazy. I'm going to donate but i'd still feel better if you didn't try to complete it if it risks injury.
I've hiked 15 miles in a single day while carrying 80+lb of gear. Didn't even take me all day to do, I had it covered in perhaps 5 hours.
If you've practiced for this and have the right equipment along with friends along the way in case anything goes wrong, its perfectly safe and can be a lie-changing experience to do.
He's got plenty of time- at a typical human running speed in the 8-12 MPH range it probably won't be much more than 2 hours a day of travelling sustained for the 10 days.