It was in December - there was only one flight to Sydney per day with Virgin. Ticket was booked via
Etihad so I had a 9h layover before my flight to AUH.
Goal was to get it done in Brisbane to have the full 9h and do something instead of waiting for the test at SYD.
I booked a second appointment for the SYD facility but this was proven to be not necessary - as they could see my BNE booking.
So I landed in Sydney and did my test there but lost some time to transfer between domestic to international with my bags, lining up and etc. Baggage check-through was not activated so that was annoying.
If you can do it the previous day it might be better ! I believe they can test you within 24h of your flight if I remember correctly.