Does the time difference between Moscow and São Paulo change during the year?

No. The gap stays at 6h all year.

When is the best time to call São Paulo from Moscow?

Between 15:00 and 17:00 in Moscow, which is 09:00 to 11:00 in São Paulo.

Moscow is 6h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.

Moscow

Russia

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São Paulo

Brazil

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

City	Time zone	UTC offset
Moscow · Russia	Europe/Moscow	UTC+3
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Moscow and São Paulo?: Moscow is 6h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Moscow and São Paulo change during the year?: No. The gap stays at 6h all year.
When is the best time to call São Paulo from Moscow?: Between 15:00 and 17:00 in Moscow, which is 09:00 to 11:00 in São Paulo.