Our experience wasn't the greatest upon arrival into AKL as we were on the 2nd flight from LA (NZ5?) and NZ1 was late, arriving just before us. Plus a Cathay flight from Hong Kong had landed between us. So three large plane loads of people trying to clear immigration together was not easy. Even the Residents queue was pretty big (may have cleared faster though). With the queue for biosecurity as well on top of all this, we must have taken around 1.5hrs from landing to being out of the airport.
If you're on the earlier flight though, you will probably avoid this hassle!
Having said that, if you're on a single ticket booked through to Tauranga, even if you miss the flight, Air NZ should look after you. Just make sure you speak to one of the ground crew when you arrive if you're at all worried about your connection time.