My suggestion is you upload a Tableau packaged workbook and show us how far you've gotten with your problem and then outline the questions for things you're stuck with.
Just did. I posted accidently before I finish typing..
It seems that creating heirarchy can solve the notional part, but still not sure how to get the median of ActualEndTime.
If I use datediff, and get an integer, how do I convert it back to hh:mm:ss format?