On the 'bus, Out is operator defined. Our company used to have the 2 knts trigger, but this gave inaccurate Out times when you had a very slow pushback. So it was changed to Park Brake release, or if the park brake is off (perhaps because the brake fans are still on), when the last door is closed.
As for Off, it's always when the Air/Ground sensing determines you're airborne
AFAIK.
One thing that always puzzles me is that Airlines are always hung up about departure time for On Time Performance when as a passenger, you are far more interested in arrival time - especially if you have a connecting flight!