how much time needed to travel around the south pacific??

i would like to go to australia-great barrier reef, new zealand-auckland, bay of islands, tahiti, fiji.
how long shoould i stay at each island for??
is a whole month enough??

I would suggest longer than a month in Australia because it is a very big country, then two to three weeks at each small island (like Fiji). I love Fiji, but the islands are very small, so you don't need as long to explore.
Oops, missed New Zealand, same as for Australia, plan on a month or longer there.
:) Happy Trails

NZ/Auckland Perspective.. If you are doing just North island you could hire a car or take tours, theres only RUBBISH public transport) a week is plenty you could get to Bay of Islands (31/2hrs from Auckland). I would recomend Islands in the Hauraki gulf out from Auckland if you are pressed for time too, a short ferry from downtown Auckland to Waiheke Island, Tiritiri Matangi Island (one of only 2 open reserves in NZ so lots of native species), and Gt Barrier Island which is very remote and runs on Generator power so 20 years behind the times). You could pop down to Rotorua too a thermal resort, and maybe even drive the Beautiful Coromandel coast with its beaches too.

Fiji and Aust Ive been too depends on your connections time but a few days for the reef and a week in Fiji each? Save more time if you want to vist the South Island, the North is Volcanic and rolling hills, the South Island is flat vineyards, and real mountain ranges...

Nowhere near long enough.

You could do it in a month however you wouldn't get to see much. I would suggest 2 months minimum however that depends on your schedule.

I spent 2 months in New Zealand alone. I also hit Tahiti and Australia going from Melbourne up and down the Gold Coast. All that took about 4 months, and it wasn't nearly enough time. Spend at least 6 months to do it right.