He starts out rowing whenever he feels like it, sometimes rowing to the excess of 16 hours in a single day.
So Amyr adopts a regular "work" schedule, rowing at most 8 hours a day, but allowing 2 extra hours whenever he feels energetic and motivated.
He then becomes so productive that he's able to cut 40 days from his initial schedule (it took him 100 days as opposed to 140 days to cross from Africa to South America).
Edit: link to the book
Get dozens of book recommendations delivered straight to your inbox every Thursday.