In the US, each vendor has their own policy. Apple has a 14-day policy, would be surprised if that were less in other countries but really don't know. In the past, they have even allowed returns during a longer period if a new model was just released and you bought the old version. If you bought from a third party, that's another matter of course.
Yes I will have a hunt around the Apple Australia website and see what I can find - not much point in worrying until we see exactly what Apple are releasing, and moreover WHEN it will be available.