Unfortunately for us crew it is not defined.
some have it on entering the crew room. Some have it car park some have it from arriving at the queue for security if your crew room is airside. It just hasn’t been officially defined by the regulator so it’s up to the operator and their unions to come to an agreement.
I’m pretty certain in the not too distant future with electronic flight logs and briefings etc it’ll become on entering the aircraft unless we fight it