I would say (I am not a Dr) that the injury you're recovering from should be the determining factor: your body will tell you "how much" and "how often".
If you're regularly riding seven miles twice a day without noticeable discomfort from your injury, then an hour's training ride seems a reasonable starting point.
I'd get comfortable with a duration, then increase the frequency of rides at the same duration; then I would increase the duration *and *revert to a lower frequency.
Periodically (at the end of each cycle perhaps), ride for a specific distance that is *less *than what you estimate you ride in your timed runs.
Whatever else you do, don't over-do it: make a plan and stick to it, no matter how good you feel. Coming back from an injury, enthusiasm can easily get the better of good sense, which risks undoing all your hard work and sending you back to "square one".
I would say (I am not a Dr) that the injury you're recovering from should be the determining factor: your body will tell you "how much" and "how often".
If you're regularly riding seven miles twice a day without noticeable discomfort from your injury, then an hour's training ride seems a reasonable starting point.
I'd get comfortable with a duration, then increase the frequency of rides at the same duration; then I would increase the duration *and *revert to a lower frequency.
Periodically (at the end of each cycle perhaps), ride for a specific distance that is *less *than what you estimate you ride in your timed runs.
Whatever else you do, don't over-do it: make a plan and stick to it, no matter how good you feel. Coming back from an injury, enthusiasm can easily get the better of good sense, which risks undoing all your hard work and sending you back to "square one".