Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Redmond to New Zealand as you normally would.
Due to multiple factors, expect to potentially pay more when booking in December. For low rates, June can be a great choice for travel to New Zealand. Flights to New Zealand from Redmond in June are about $1,259 on average during June, but can be found for as low as $779.