Excerise to treat or help hamstring tendonitis. I'm athelete how long should I wait to run again?

Patience. If it is hamstring tendinitis, allowing it to heal completely before resuming your training regime is best. Oftentimes in my practice, patients may return to play too soon and then it becomes a lingering issue for some time. Generally speaking 4-6 weeks should heal it. I would suggest another activity in the interim. Perhaps stationary bike if that does not irritate it.