In the terms and conditions for Koru members (
http://www.airnewzealand.co.nz/koru-...ccesstolounges) it is restricted to prior to departure:
Members must present their Card and a valid Air New Zealand boarding pass or ticket for an Air New Zealand ticketed and operated flight on that day which has not yet departed from that airport.
For gold / gold elite (
http://www.airnewzealand.co.nz/frequ...e_privileges):
Gold members have access to all Koru Lounges within New Zealand and all Air New Zealand operated International Lounges prior to departure.
Gold Elite members enjoy the same lounge privileges as Gold members
So you may be able to enter but it is subject to the lounge guardians.