Does the time difference between Dubai and Sydney change during the year?

Yes. Because of daylight saving time the gap moves between −7h and −6h.

When is the best time to call Sydney from Dubai?

Between 09:00 and 11:00 in Dubai, which is 15:00 to 17:00 in Sydney.

Dubai is 6h behind Sydney. This gap is not fixed: daylight saving time moves it between −7h and −6h during the year.

Dubai

United Arab Emirates

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Sydney

Australia

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A 9-to-5 day in each city overlaps for 2h. That is 09:00–11:00 in Dubai, which is 15:00–17:00 in Sydney.

City	Time zone	UTC offset
Dubai · United Arab Emirates	Asia/Dubai	UTC+4
Sydney · Australia	Australia/Sydney	UTC+10

What is the time difference between Dubai and Sydney?: Dubai is 6h behind Sydney. This gap is not fixed: daylight saving time moves it between −7h and −6h during the year.
Does the time difference between Dubai and Sydney change during the year?: Yes. Because of daylight saving time the gap moves between −7h and −6h.
When is the best time to call Sydney from Dubai?: Between 09:00 and 11:00 in Dubai, which is 15:00 to 17:00 in Sydney.