I have had the pleasure of using the SQ lounge in SYD on a couple of occasions recently. It is usually pretty empty when I use it as their last SQ flight departs at 19.10 but they announce boarding before 6. The lounge then closes at 6 though the staff don't expect anyone to be around then. That is usually ok as my WLG flights are around 18.30.
The beef rendang is quite tasty, too.