At this point in time the Qatar airlines website is still showing that there is no access to the Plaza premium lounge (or any other lounge at Brisbane's international terminal - although none others open at 10:40pm QR's departure time).
QR's worldwide lounge website:
Access to the Brisbane airport QF lounges should be easy given you're departing on a one world flight and hold one world status. The last Qantas departure from Brisbane on that Friday is a 9:20pm flight to Darwin so I'd expect the BNE domestic lounges to be open until about 9pm.
It's also worth noting that the Plaza premium lounge is a pay to access lounge, this can be rebooked on the Plaza Premium website for $49 for 2 hours per person or a better value option is via the Dragon Pass app (there are ways to get a free membership - mines via Regus) where 3 hours access is 19GBP (works out at ~AU$33 per person).