Last winter (July) I was able to go to Sydney, Cairns, and Melbourne. This year, I have about 2.5weeks or so to plan it out. I can either fly into/out of SYD or MEL. I want to go to CNS for 4 days on the reef diving again - that was a lot of fun.
But where to go? Perth? Adelaide? Maybe Hobart? Maybe a day or two side trip to Papua New Guinea? Could do SYD-CNS-POM-MEL/SYD (but the CNS-POM seems a bit pricey) or SYD-HBA-ADL-CNS-SYD/MEL
SYD I don't think more than a day or 2 as I have already seem it and around it (parks and stuff)
MEL also a day or 2 should be more than enough
CNS can get tricky, as if I try to go diving, I would need to either spend the night on the return of the trip at a hotel and fly out the following morning to decompress, or like last time just snorkel on the last day and grab the last flight out at night (which we took to MEL). If I did a 4day/3night diving or 3day/2night I have to add a night before that (as theres no way I can get to CNS dock by plane before 7am boat dept)

Edit: Seems I got a room on hold in Port Moresby in Crowne Plaza. Can get the diving in there, if possible. If not I can always cancel it.