You could do a 2 3 2, which is 2 days in Sydney, three days somewhere else, and 2 days back in Sydney. When you say Dive, are you talking about the Great Barrier Reef?

In May, summer is pretty much over and the water should be warm still. If you want to dive, I would go for it, but it will be quick.

I will be in Sydney this coming may, and I expect to be wearing a jumper if not during the day, but at night.
You need to get yourself up to Queensland for May, to enjoy diving.

so apart from sydney, should I go to Gold Coast, Cairns or just Hunter Valley / Nelson Bay etc?

Grateful for your input!

Hi jyeung - If diving is important to you then get up north. You can, of course, dive around Sydney - but if you want warmer then north you should go. Get yourself a good travel guidebook and a cheap flight.

If diving is not that important then you could easily spend 3-4 days in the city assuming you like to wander, and soak in the atmosphere of a different place. Day trip to Blue Mts easy to organise. Ditto Port Stephens/Nelson Bay tho best to stay overnight. Let the train take the strain - and to PS there's always the bus.