Given the sale at the moment and seeing that today is the last day, of course YMMV as far as locating the lowest prices for those sectors. The main things are:
- Use the multi-city engine (domestic) to reduce your c/c charges, i.e. squash as many sectors in the same itinerary. This does place limits on the itinerary, for example, can't have more than 4 different locations, can't repeat the exact same sector (intentionally). You also can't have more than 2 selected flights per day, but you can get over this easily by choosing "Flexible with Dates".
- When using the multi-city engine, use origin-destination as BNE-ADL or ADL-CBR or vv as necessary. Don't type in BNE-MEL then MEL-ADL or ADL-SYD then SYD-CBR; that won't work.
BNE-MEL-ADL-SYD-CBR can be achieved in 1 day; the other half the next day. As I said, you need to overnight with this run, which reduces its "real" value (although mitigated if you have contacts in CBR). Also, I did these runs on the weekend. Weekends have less flights, and the "return" flights on Sunday can get very expensive - this may require lots of searching and re-searching to locate flights that are at their cheapest.
The turnaround times can vary. Sometimes you'll have a decent margin up your sleeve; other cases it'll be bare MCT of 40 minutes.