Hi !
Mmmmmmm well flight time starts when aircraft moves on it's own power, but pushback is taken into consideration I think. What do you fill in your techlog as block off ? What does your ramp agent write on the papers ? All the 3 timings should match anyway... You cannot have your block off for the pilot's logbook, the block off for the techlog and the block off for the ramp. In my carrier starting pushback means off block.