Firstly, I absolutely agree with all of the above - 1hr scheduled time from international with checked baggage is recipe for disaster.
That out of the way, it might be worth pointing out that Air NZ do like to give themselves leeway with scheduled arrival times, and if you take a look at flightaware for your flight:
http://flightaware.com/live/flight/ANZ776
It will show you that when it leaves on time, it usually gets in around 18:00 rather than 18:30.
Does that change my first opinion? No. But an interesting (or not, you tell me) point nonetheless.