Sydney and Brisbane are usually on the same time, but Sydney is 1 hour ahead during daylight saving. Both use Australian Eastern Standard Time (AEST, UTC+10), but Sydney observes daylight saving time (AEDT, UTC+11) while Brisbane does not.
From early October to early April, when Sydney is on AEDT, it's 1 hour ahead of Brisbane. The rest of the year, both cities are on the same time.
Any time works! With at most a 1-hour difference, you can easily coordinate calls during normal business hours (9:00 AM - 6:00 PM).
Sydney and Brisbane are Australia's two largest east coast cities. The flight between them takes about 1.5 hours, and the Sydney-Brisbane corridor is one of Australia's busiest domestic routes.