My 13.4 miles section can be done as fast as 45 minutes, or as slow as 1hour and 15 minutes. When I am really rested, I will blast it at speed which I can sustain for 2 hours. When I am feeling the tiredness of leg, I will just go at fat burning zone or recovery zone ride. I just alternate around. Usually 2 days of harder ride and 3 days of easier ride.