I'm retired USAF as well. Best advice -- have him sign up for the flight back as soon as he arrives. Then when he gets ready to go, he can check his status on the list. If his "number" has been passed over (he wasn't in the terminal when he was called), that puts him at the top. If his number hasn't come up yet, he just has a bit more waiting. Best, though, is to waiting in the terminal during the day (most flights come in then), and then returning to your house to sleep. They (clerks at terminal) might tell him it looks like another day before his number will come up, but suddenly a flight can divert from elsewhere and there are lots of open seats, so staying in the terminal as much as possible (when he's ready to go) is his best bet.
I've had good (quick) waits, and very long waits. The worst was sitting at the terminal in Rhein Main for . . . (drum roll) . . . seven days. By the end of it, I wanted to have my mail forwarded and take a class or something. Argh. Had nowhere to sleep (billeting was full), and when I finally got my seat, I slept the entire flight back to Philadelphia.
Best of luck!