determine total overlap time when there are gaps in overlap (4 date ranges)

Good afternoon,
This is my first post to excel forum; thank you in advance for any assistance.

I have rows of people and columns with start-end dates of 4 different medications (9 columns total, see example attached). I need to do 2 things:
1. Determine if there is a gap in coverage between medication. As long as the coverages overlap in some way shape or form, that's good: I need to know if there is a time frame between first start date and last end date where there is no medication ordered.
2. if there is a gap, I need to calculate the total coverage time for any/all meds that DOES NOT incorporate the time of gaps in medication ordered.

I can;t figure out how to address the gap (if there is one).