If the Jan incident happened as posted by the pax, then as I understand it- no breach as they obviously got clearance and taxiied before the cutoff.
Back to dispensations- I recall one occasion a couple years back where due severe weather disruption we sat around for ages, going, not going, going, not going (thankfully we were on a/c and pax in terminal with access to facilities)
Eventually it was decided (by local authorities I guess) we could break the curfew and depart, due to no rooms available anywhere for pax or crew. Loaded everyone on, doors closed, ready to push back... oh wait permission revoked.
Long story short the "rescheduled" flight for the next morning ended up being further delayed because with the thousand or so pax dumped into Sydney, there was no transport (company transport stretched so private transport booked).
It failed to turn up for nearly 2 hours, by the time we got to the hotel we'd well and truly busted min rest (which in this case could be reduced to I believe 10hr for the CC) and ended up sharing rooms. I think the pax slept in the airport. So for the sake of a 737 not making too much noise we were delayed in total over 15hrs, the aircraft and crew were out of position in Sydney instead of Melbourne and the subsequent day's flying had 2 legs cancelled and the rest severely delayed. 2 of the crew were on legal days off so had to passenger home on the same flight rather than operate and we copped further delay waiting for replacements (as they were all in Melbourne due to not being allowed to land into Sydney the night before)
So yes I agree, flexibility needs to be there and more consideration given to the knock on effects of keeping a flight on the ground. (In this case it was firstly ATC delay in MEL then severe, hours long tx delays in Sydney)