We average about 60 - 70 minutes an ADR (not including any transportation that may be needed).
I will often overlap an ADR time with the intention of tapping in at the later portion of the window. That way I can hit up the 2nd FP window almost right after it.
For example, if I have a 12:30 ADR at CP in MK, I may do a 1:15 - 2:15 FP for Peter Pan and then 2:15- 3:15 for Pooh. Most likely I will get to PP between 1:45 and 2:00 and then I can catch Pooh at the start of it's window.