It depends on the what the customer airline requested when ordering from Airbus, the oldest aircrafts in our fleet generate an out time when the brakes are released(hence our SOP call for placing zeros in the Flight number/AC line number fields in ACARS to help prevent false in/out time being registered in the system), others when cabin door is closed and brakes released, and the newer A320/A321's which weren't second hand is based on groundspeed greater the 3kts , later MSN on combination of engine start and brake release, its all set to what the customer requests as for triggers of out time.