Low level risk so long as you can arrive into ADL - say 12 hours prior. But to avoid the early SYD-ADL departure, just organise an overnight in Adelaide and do the whole trip with minimal stress.
In post 5
babyg_wc was considering 3 hrs.
The consequences of missing a long haul business class award for 2 pax are significant. The QR flight has ~22:20 departure time.