Just an update on my experience last week:
-Immigration took about 30 seconds with lots of lanes open and only our flight goign through at the time
-Bags were reasonably quick - I'd say 10 mins or so for them to come out
-Customs was also very quick probably at most 2 minutes. And customs agents were super friendly to everyone

I'm glad I didn't book the connecting ticket though. My DJ flight from HIR was 1:30 late so I would certainly have missed my connection. With 18 mins to the next train I went upstairs to the QF international sales desk, and bought a ticket to SYD there (it was a good deal, too).

To answer my question, even if my flight had arrived on time, 1:30 would probably have been tight. But I found BNE to be an easy airport to deal with. Inter-terminal transfer could be an issue but it wasn't for me.