Remembering what the legislation states, I interpret it to mean
the total time from the moment at which the aircraft first moves under its own power for the purpose of taking‑off until the moment at which it comes to rest after landing
I taxi from the hangar to the fuel bowser, shut-down, refuel then taxi back to the flight line. Log-able as flight time or not?
You weren't taxiing to take off, so no not logable
I taxi from the hangar and idle for an hour at the holding point then taxi back and shut down. Log-able as flight time or not?
You were taxiing for take off (I assume that's the scenario, not that you were going to the holding point for fun) and the runway closure/mechanical problem, causes you to come back, it's logable.
