Also, FWIW, when you deviate, they then calculate per diem based on:

If DH was at the end of a trip: they will then use the first flight out to your base, regardless of legality. So, if you get in to IAD at 6 pm and your DH was for noon the next day, but there was a 6:10 pm flight out that same night, they show you on the 6:10 flight.

Same idea for the front of the trip, even if the new flight gets in 10 minutes prior to show

Not that big of a deal, but could cost you $40 non tax money