I wonder if what you're thinking of is the relatively common practice of adding 0.1 to flight-times, to allow for taxi-times at the start/end of a flight. A practice that as far as I'm aware is quite legal.
Now, it's been a long time since I studied aviation law -and then, that was in NZ; but within the CAR's, there used to be -as a definition of loggable time- words to the effect of:
"from the time the aircraft 1st moves under it's own power for the purpose of flight, until the aircraft comes to rest at the end of that flight". Given that most operators record aircraft total-times, MR flight times etc. on squat-switch timers, tacho timers or pre-determined block-times, the practice of adding 0.1/0.2 to those times
where appropriate is both legal and bl@@dy nearly
mandated in law IMO!
One thing I can freely guarantee you right now is, your question is going to be the catalyst for some pretty serious and robust debate here -starting any minute now
Grab some popcorn and settle in for the entertainment!!!