As above, if separate tickets/PNR it is all at your own risk.
QF723 is the only QF flight from ADL to ASP per day
Virgin have a flight VA1741 at 13:50., but not every day. VA are a ff partner of SQ

ADL is a small airport. International & domestic flights arrive/depart from the same building

Looking at the history of SQ279 sometimes it a little early, but at other times has been late by 15 -30 - 85 minutes.
https://flightaware.com/live/flight/SIA279