Originally Posted by Kiwi Flyer

You should miss the worst of the holiday weekend traffic (Friday afternoon leaving Auckland and Monday afternoon heading back to Auckland).

Weather forecast can be found on the metservice site, but remember weather forecasting in NZ (especially mountain areas) is notoriously difficult. It has been wet lately with heavy downpours in the northern North Island interspersed with some fine days. Queenstown is very cold with snow on some days - I hope you are flying Air NZ down there (better chance of arriving on the day you booked).