Average # of Days (or Cells) in a Table

Good Morning Experts! Hoping someone can point me in the right direction. I have a schedule with Start and End dates and "x" or "h" to indicate if someone is on call for that week. Using a random name generator to mix up the names, but I want to make sure everyone has about the same amount of time between duty weeks. Looking for a way to easily see the average, number of days between each on call week. That way I can look and say Joe averages on call about every 6 weeks. Hope this kind of makes sense. Open to any ideas (formual, pivot, macro, etc)....Sample attached.