When is the best time to apply for a METV at the Sydney consulate?

for all METV's ( Multiple Entry Tourist E–Visa ) from all Thai Embassies/Thai Consulates:

a 6 month METV starts running down the 6 months from the issue date, NOT the date you first enter Thailand on a METV

if you are going to obtain a METV, then get a METV as close to when you are actually traveling to Thailand as you can; otherwise, you lose time on a METV by not being in Thailand

Probably about 2 weeks prior. Sydney is not known to be a long process embassy like France or Germany. You don’t want to apply too early as you’d lose time from the METV validity.

Ensure you provide proof of needing a METV over a SETV otherwise they may issue the latter even though you’ve paid for the former. Usually proof of flights in/out and back in again is enough.

That makes no sense but it is Thailand