Going to depend greatly on weather, availability (you, instructor, aircraft - all at the same time), proficiency with exams, and how quickly you can spend the money.
But as a guide, a full-time CPL typically takes a little over 1 year - includes PPL, CPL, CIR (total about 200 hrs).
Just a PPL when flying regularly and you're ok at exams - I'd guess 1-2 months would be doable, perhaps 2-3 realistic. The basic "theory" study will take significant time (couple of weeks, maybe) and must be included. A typical one-flight-per-week PPL takes about a year!
(If you can fly 2-3 days a week, flying progress will be good ... but 2-3 days can become 0-1 days if the weather gods are unfavourable.)
Things that will cause extra delays: CASA processing (they're snowed under issuing Part 61s at the moment, everything seems to take longer); medical (issued by CASA); acquiring books, charts, etc. Some of those can fit around the flying, but be aware of time required.