According to an email Mattw received from Ticketmaster:
This is a courtesy email regarding the Tool concert at the Sydney Entertainment Centre on the 24th of January.
Please note that Tool will perform the entire show and are expected to be on stage by approximately 8:00pm. There will be no support act.
RUNNING TIMES (Time)
Ticketed Start: 8:00pm
Main Act: 8:00pm-10:00pm TOOL
Please be aware that these running times are approximate and may change slightly.
I very much doubt that they will really start at 8. Getting 12,500 people inside in time for Tool to start at 8pm just doesn’t compute. Expect the actual starting time to be closer to 8:30. I’d still suggest you turn up to get in at 8pm anyway, or maybe a little before just to be safe.