Southern-hemisphere DST is inverted, and nothing warns you
From late March, when Europe springs forward, to early October, when Sydney springs forward, the offset between London and Sydney ranges from 9 hours (London GMT, Sydney AEST) to 11 hours (London BST, Sydney AEDT) across the year. For two weeks in April everyone on both sides shifts at different times, and the recurring call that worked in January suddenly happens at a different hour in April. If your team includes anyone in Sydney and anyone in Europe, this is the single most important thing to put on a shared calendar with a loud warning — because none of the calendar apps will flag it for you.
Five Australian zones, but most business happens in one
Australia runs five time zones: Western Australia (+8), Central Australia (+9:30, with its own separate DST decision), Eastern Australia (+10 and +11 with DST), and Lord Howe Island (+10:30 and +11 with a rare half-hour DST). For practical business, Sydney, Melbourne, Brisbane, and Canberra dominate. Queensland stays on AEST year-round because the state never adopted DST — too tropical for the rationale to land — so in summer there's a one-hour gap between Sydney and Brisbane inside the same country. Northern Territory runs +9:30 year-round.
Earliest Monday on Earth, except for Auckland
Sydney is one of the first major business cities to start the work week — only Auckland and a few island nations come earlier. When it's Sunday 9pm in New York, it's already 11am Monday in Sydney. For a global company, this means the Sydney office owns Monday mornings and often flags weekend issues that the rest of the world will pick up hours later. It's also the city most likely to have a working answer when London wakes up on Monday and wants a status update. That's a genuine structural advantage — use it deliberately rather than accidentally.
Best call windows
Concrete time slots that work for synchronous meetings between Sydney and common counterpart zones. All hours respect daylight saving automatically.