FR24 departure / arrival times.

[25F]

AIUI stated departure / arrival times are pushback from the gate and arrival at the destination gate i.e. wheels start rolling to wheels stop rolling. Although I have read a suggestion that departure is cabin door shut and another that it's chocks removal. And that this might depend on the airline. Either way, FR24 is quite confusing in that it gives ATD as time of takeoff (again, is that throttles forward or actually airborne - not that it makes much difference). It does at least give the arrival time as "landed".

[DaveReidUK]

Just get used to it.

The industry uses 4 times, commonly referred to as "OOOI".

Out: when the aircraft starts to move (i.e. usually pushback, also referred to as "off blocks")
Off: when the aircraft takes off
On: when the aircraft lands
In: when the aircraft comes to a halt at the gate (also referred to as "on blocks")