It's more or less a domestic flight BUT since you check your bags in (assuming you have such) at the domestic counters for international flight connections this will require a couple more minutes for document check etc.
But you don't need to arrive stupidly early for the connection. I would plan to arrive 0600ish for such a flight. That is a fairly lengthly connection in SYD if connectring to the 1200 QF11 since you'd land in SYD between 0830 and 0900 or so, so more than enough time to transfer over, go through international departures and then lounge, shop etc.
Back to MEL check in, I've never seen huge queues taking a lot of time, but to be extra safe you'd probably want to allow for 20-30min "just in case" - it may only take 5min, but having that buffer can be everything and if you have that extra 20minutes, time for a coffee before boarding.
I will relate one experience, and do NOT try this at home (well, at the airport
) kids but it this one time, due to transport snafus and the like I arrived at MEL I think 25 or so minutes prior to departure of my flight to SYD to connect to an international. LUCKILY I had HLO and the agent did barely allow me. I think only my status saved me, to be honest as they were half way to closing the check in for it. Rushed through security and ran to the gate and was probably puffing through taxi
that was a VERY close call that I do not recommend (and for the record, there was not much buffer to just get the next SYD flight as it would have been too tight going through departures there!).. not a situation I would ever want to repeat though.
So anyway to be safe, if it was me, I would aim for an hour prior. a bit more is always good. better to be bored with a coffee than to miss out (though if you miss a 7am flight connection there would be plenty to get to SYD in time anyway, but you still don't want to play that game).