XPT, I'm not so sure about that.
In summer flights are still happening at 8pm local. Local business people complain that in winter they can't do a full day's work in Auckland or Wellington and get back home the same day.
And spreading out the international arrivals would be a good thing. On weekends in the ski season the airport gets quite congested as all the flights from Australia arrive within a short period during the afternoon.
BNE1320, passenger numbers to ZQN have been growing steadily for years now, especially international passengers, who are not necessarily Australian. Why do you think there will suddenly be a big drop in demand?