Don't get too excited, Excited one,
To my knowledge is has taken guys joining as S/O's at least six years to get based down in Oz. S/O's are not eligible for bases, other than the rare temp base offering. You must first jump through sufficient hoops through JFO to F/O before you are eligible for a base. And if you are considering joining CX just to get an Oz basing, you should think again. The number of aussies who have joined CX in the last few years is a !!!!load, and there will only ever be so many slots down there.
So to answer your question, you can get a basing down in Oz very easily, just as soon as you get a job with Qantas.
Good luck