Just jump on the first bus to MK at AKL, that will drop you at MK bus depot. Find out what bus stop the Beach Club is and take that bus to that hotel, get off and walk to IG entrance.
The bus ride will take approx. 1/2 hour so I would arrive around 8:30 to 8:45.
This gives you enough time to Skyline, Friendship boat or walk from HS to IG.