Nobody can keep track of Australia's time zones
In winter
New South Wales, Victoria, Queensland, Tasmania GMT+10 hours
South Australia, Northern Territory GMT+9.5 hours
South-Eastern Western Australia GMT+8.75 hours. (The little known Central Western time, so obscure that many people are aware that it exists. But it does).
The rest of Western Australia GMT +8 hours.
In summer
New South Wales, Victoria, Tasmania GMT+11 hours
South Australa GMT +10.5 hours
Queensland GMT+10 hours
South-Eastern Western Australia GMT+9.75 hours.
Northern Territory GMT+9.5 hours
The rest of Western Australia GMT +9 hours.
All that for barely the population of Holland.
Daylight savings time is deeply controversial in both Queensland (which presently does not do it) and Western Australia (which presently does), so this may change. In addition (as this article indicates), starting times have been varied over the years, sometimes unilaterally by individual states, meaning that although Sydney and Melbourne theoretically use the same time in both winter and summer, there have been occasional periods in winter and automn where they don't.
And don't get me started on Australia's many railway gauges.