Does the time difference between Melbourne and Moscow change during the year?

Yes. Because of daylight saving time the gap moves between +7h and +8h.

When is the best time to call Moscow from Melbourne?

Between 16:00 and 17:00 in Melbourne, which is 09:00 to 10:00 in Moscow.

Melbourne is 7h ahead of Moscow. This gap is not fixed: daylight saving time moves it between +7h and +8h during the year.

Melbourne

Australia

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Moscow

Russia

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A 9-to-5 day in each city overlaps for 1h. That is 16:00–17:00 in Melbourne, which is 09:00–10:00 in Moscow.

City	Time zone	UTC offset
Melbourne · Australia	Australia/Melbourne	UTC+10
Moscow · Russia	Europe/Moscow	UTC+3

What is the time difference between Melbourne and Moscow?: Melbourne is 7h ahead of Moscow. This gap is not fixed: daylight saving time moves it between +7h and +8h during the year.
Does the time difference between Melbourne and Moscow change during the year?: Yes. Because of daylight saving time the gap moves between +7h and +8h.
When is the best time to call Moscow from Melbourne?: Between 16:00 and 17:00 in Melbourne, which is 09:00 to 10:00 in Moscow.