Mid morning and later at night.
You could phone QF up and ask on all our behalves!
But it can still go pear shaped, even if the bus is "supposed" to leave in 10 mins.
Don't believe the staff member who scans your BP (issued in ADL, (lets say) at SYDd going to the bus gate 15.
The bus can sit there, for another 5 or 10 mins, even if the bus driver is standing there.
For the OP, I would really try to even get to SYD the previous night. Edit: I see, they won't change you ADL - SYD direct..., ok, it will be hard this time round, even getting to SYD earlier, but if there is a next time, try to get to overnight in SYD. $$$ I know, but better seeing this is a big trip.
Playing around ADL - MEL - SYD - SCL is fine, on spreadsheet or on paper planning, but as you have seen, QF can change things to a drastic degree.
Ok, some of you don't like my waffle.
I did ADL - SYD - WLG or CHC last year, in J. Not exactly sure which one I did not make it to the QP, either of WLG or CHC anyways, (I did them both a few days apart).
The plane I got was that 717, left ADL at 13.45, got to SYD at 16.00, plane to WLG/CHC was to go at 17.45 or so.
The bus sat at SYDd till about 16.20! I was worried, a lot of others on the bus were as well.
Made it to SYDi at 16.45, ran from bus up that long stair case, up to Immi and int security, did not make it to use the QPi as I didn't have time, though I had QP membership.
From now on, as I plan to keep my QP (pay after my SG runs out), I will do a separate PNR, even if I have to fly Y ADL - SYD the night before, and do a J SYD - NZ!
It does help that you will be given a BP for ADL - SYD - SCL, and an OPC in ADL, bypassing SYDi check in, and that the QF bus goes airside, but still, a lot too much can go wrong.