Hamstring Injury From Distance Running

I am 55 years old and a long-distance runner. I had a hamstring injury about 2 years ago that took a couple of months to heal even with physical therepy. I have had a recurrance of the same injury 5 days ago. I have stopped running and am following a general process of self-treatment. I would like to recover faster than last time.

My questions are:
1) Does cross-training on a mountain bike prolong the recovery? I did that last time and have developed this suspicion after reading my notes.
2) Can I run shorter distances, say 5 miles without prolonging the recovery? My normal distances are between 10 and 20 miles.
3) How about slow long distances?
Any other advice will also be greatly appreciated.