I just came from my first physical therapy appointment and was looking for a similar app. I need to get up every two hours and do a back exercise. I am trying an app called Calendar Snooze. I made a calendar entry called Exercises for when I wanted it to go off the first time, and I plan to snooze it every time it goes off. I've already verified that I can snooze it for two hours. So far so good, so I thought I would share.