If you're not transferring to another international flight, then you won't be able to access the RCC. It is airside in the international terminal.

To make an Intl-Domestic transfer, you will need to exit Immigration & Customs and then get over to the domestic terminals. The options are a train ($7 AUD last I checked) or a tax for $10+ depending on time of day. I wouldn't do any less than 2 hours. 3 to be safe.

If you fly with DJ, then you can buy a one time pass to their lounge for $30 AUD. QF/JQ doesn't have this option.