Currently the DFW flight is leaving around lunchtime in Sydney - sadly they offer a single "(small) plate" "supper" service. (So check what availabe to eat in the Lounge Qantas provides.)

Personally, ex USA, I'm not sure about "slow service", IME they work proactively to get everyone to sleep ASAP, even though it is still afternoon/evening in MEL/SYD/BNE.

I have seen the slow service ex Oz though - worst to date has been the HNL flight where I received my appetiser 2 hours after departure.