Accessing the lounge
Your lounge access is valid for up to two hours prior to departure, however it doesn’t cover connecting or arrival lounges. When you arrive you’ll need to provide your lounge access confirmation email and a form of photo ID/Senior’s card. Lounge access is redeemable for all domestic economy flights at any of the following departure locations: Sydney, Brisbane, Canberra, Melbourne, Gold Coast, Darwin, Cairns, Alice Springs, and Mackay. Complimentary access to the lounge will be valid for travel between May and June 2016.
from the T&C's
"...Only one Lounge pass per flight per person is available. This offer permits guests to enter the Lounge 1 hour prior to flight departure only. Entry to the Lounge for Single Entry is subject to space availability and may be restricted during peak periods and when the lounge is at or nearing full capacity..."
might pay to confirm directly if you are using this offer.