Don't overcomplicate things.
You could use an approach similar to c25k with the bike, except keeping a steady pace.
Start by riding 3 non-consecutive days per week, at 30-40 minutes per ride. Slowly ramp up your distance/time, then ramp up frequency.
It's not rocket science. If you want to ride your bike, go out and ride it. If you're exhausted and don't want to ride, stay home, don't make something fun start to suck because you're forcing yourself to ride and over analyzing everything.