From a passengers perspective, and the applicability of R261/2004, it is better to have a definition that a passenger can relate to.
"Pulls on the stand" or "Block-to-Block" or other airline/atc jargon are unknowns to a passenger. Door opening is more likely to be understood, although if you are in row 76 it could be another 10 minutes until you have actually 'arrived'.
But, IIRC, it hasn't been airline practice to record 'door-opening' times. Has it?