Immigration opened 4:30am on the dot, they use Smartgate for departures as well.
After getting through Emigration and Security, surprise surprise there's a Duty Free walk through - head tight through on the right to find on the other side the hallway for the entrance to the AirNZ International Lounge.
Originally in row 1 both ways, for MEL-CHC, Row 2 was empty and I bailed to there before takeoff.
It seems that from Monday, the only area (that's open overnight) to crash will be the arrivals hall immediately you come out of customs.