Since Brisbane is on the coast, I am reading your description to say that you are "four hours north of Brisbane, on the coast." That would put you around Gladstone, as opposed to due west, towards someplace like St. George.
That's an important distinction, because along the coast the ocean will moderate both the high and low temperatures, whereas inland it would likely get too hot in the summer and too cold at night in the winter.
Please feel free to correct if my assumptions are incorrect.
In any case, you should see significant growth within the first year. If the fish can survive in the pond overwinter (I realize it's the height of summer for you right now), you should eventually have some spectacular specimens. How big is the pond, anyway?
Over at aquamojo.com, in the photo section, someone posted a picture of a Green Terror he caught from a large pond system in Hawaii. Look at that and compare it to the photos of "normal" tank-raised GT's to get an idea of what kind of extra-special growth you are going to see out of this.
Your pond might run out of guppies and pollywogs, however. Hope you have a lot of insect life where you live, too.