It's probably worth warning you that Auckland Airport is ridiculously poorly served for transport into the city. The cheapest method to reach the city would be the Skybus, and that's $16 each way and takes 30-40 minutes depending on traffic. Provided the entirety of what you want to do is wander up and down Queen Street and attractions very close to it and don't mind paying $32 for the privilege, this might be OK. If you were planning on checking out things like museums, galleries, parks, etc, you will not have enough time.