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12 miles today and yesterday with the bike with no ill effects.

Just to play Devils advocate here, have your run you rehab workouts by your doctor or a certified sports trainer?
Everything I've learned or my degreed trainer friend has told me over the years tells me that working the same muscle groups on consecutive days is a recipe for disaster.

The muscles you use biking have opposing muscle that need working too.
Over develop/work one group, the opposing group can't do it's job.
You wind up with instability in your joints and that's the last thing you or anyone especially with orthopedic concerns needs.

I think I would get a trained expert to tell you exactly what muscle groups your using biking, then find an activity that works the opposing muscles. That way you can work-out everyday without overdoing it or risking long term damage for short term gains. I'd include a stretching session AFTER every workout and a rest day or two in there as well.
This morning on the CBS news they had a segment about " aging" exercisers,
The expert said that you need 3x things to exercise safely.
A baseline of over all muscle strength, same for cardio and you have to be/stay limber.
They also said that the older you get the flexibility becomes more important and in their opinion it was more important than the others to avoid injury.