depends...personally my muscles fatigue and recover on 3 days cycles, and that's typically how I train for endurance events. To be more specific, I go hard on days 1, 2, and 3, then rest for 1-2 days to allow my muscles to fully recover. Whatever I can do in that 3 day period is usually a little above my total distance potential.

To give you an example, I prepared for a marathon by regularly running 10 miles/day 3 days in a row, 1-2 days of rest to heal muscles, then repeat. Because I knew I could run 30 miles before allowing my muscles to fully recover, I felt prepared (at least mentally) for a full marathon, Now, I do my 40 mile commute, really fast and hard on Mon,tue,wed, rest thur (either work from home or carpool, drive if no other option), then go hard again on fri, then do light stuff on the weekend to recover

As you might expect, right around the time I was able to do my 40 mile commute 3 days in a row, was around the time I attempted and completed my first century. Could I have done it earlier? Maybe...is this 3-day calculation accurate for me? Maybe...Would it apply to everyone? Probably not.

I hope that helps at least a little