You'll also be able to use the Qantas F lounge over in TBIT, a short walk via the airside connector from T4. But agree, allow yourself 20 or so minutes to get to the Nest. I usually leave about 50 or so minutes before departure from QF F to the nest as I'm always flying Eagle back home to SFO.

If you're in Y you'll probably also get a free alcoholic drink during the service because FAs can't distinguish on their tablets between EXPs and OWEs (both show up as green)