I've been on an unbroken rowing streak (Concept2) since December last year. Half hour per day mandatory, no rest days. Typical distance rowed is 6.5-8km. There are days where I "take it easy" but I still force a minimum distance of 6.5km regardless of how long it takes. My rationale for using the C2 is the lower impact and the fact that it resides inside a climate controlled building. These factors help reduce the possibility of excuse making.
I found that taking even one day off is all it takes to throw my discipline into a death spiral. Making it a required thing no matter what changes the psychology and game theory. It has become entirely a background concern after day 90 or so. There are days where I have to row and then do hours of yard work. The first two weeks of Texas summer almost got to me. But, this too has become a background concern. I can wake up, row 30 minutes, landscape for 2 hours, and then write code or post on HN until the sun goes down. No naps, stimulants or motivational speeches required.