An known experience and fits:
1: the booms of the de-icing trucks are already extended in preparation for de-icing the aircraft (with the expectation for the aircraft to stop on the designated line_. This would in theory expedite the de-icing start/finish time, and subsequently creates a shorter withdrawal time, and should not impact greatly on the ETOT.
2: the aircraft, as displayed in the pictures, has gone past the stop line, as such impacting the extended booms if the above scenario is correct.
As such, the boom operators, would start the de-icing spray almost immediately as the aircraft stops, as the aircraft would (in theory) have been in contact with the de-ice ramp radio comms and have already instructed the operators on the de-ice requirements.
Maybe a little bit of commercial pressure on not delaying aircraft during de-icing so-as the operators (airline) cannot blame the airport for subsequent delays. (IMHO)