Two things
1. SYD is all day checkin, at least on the F counter
2. Other ports like MEL, BNE etc which have limitations is only are only on checkin, if you have a through checked bag,on the same day it will be checked through. Only limitation is sometimes the flight is not “open” for border checking, which is usually a quick phone call.

if the “domestic” flight is from the intl terminal and your bags are interline, there is no need to pick up, as you should be processed at your final intl gateway, which would be PER. But QF due to PER staffing have been wildly inconsistent on this. I would probably just go straight yo transfer or the F lounge - where ever the QF staffer is, and give them the bag tags. As they need them anyway.

KF