Every airlne's ACARS is different. I log OUT to IN. For our ACARS (we don't have PUSH), an OUT is generated when all the doors are closed and the brakes are released. An IN time is generated when the brakes are set and the main cabin door is opened. That's a little misleading, it actually captures two times for IN. For FAR legalities and DOT, it captures the first door. For pay, it captures the main cabin door.