Joining the line at 90mins prior to departure should get you checked in without any problem. As they show each week on channel 7 airways, it all closes at 45mins prior.
There's usually several 'final calls' too, asking for anyone still to check in for the soon to be departing flight, to join the express queue on the side.
The poor old (young) check in staff are just following the rules I'm afraid, so the 30 min turn arounds work, and the aircraft can get away on time. Which btw, that Syd flight departed on time, and with a greaser landing at the other end.
