Is the 3 hour checkin before departure for real?

For an 07:30 departure that's rough - this is for MEL-SYD-LAX-BOS on Qantas then AA. Can we reckon on arriving about 90 mins beforehand in real life, which from near Southern Cross station would mean boarding the Skybus about 05:30?

(it's not me travelling, the traveller has no status with any airline, if that is important)