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

No. The gap stays at 12h all year.

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

There is no overlap between standard working days, so one side has to call early or late.

São Paulo is 12h behind Tokyo. This gap is the same all year — neither city shifts its clocks relative to the other.

São Paulo

Brazil

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Tokyo

Japan

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A 9-to-5 working day in São Paulo does not overlap one in Tokyo at all — somebody has to take the call outside office hours.

City	Time zone	UTC offset
São Paulo · Brazil	America/Sao_Paulo	UTC−3
Tokyo · Japan	Asia/Tokyo	UTC+9

What is the time difference between São Paulo and Tokyo?: São Paulo is 12h behind Tokyo. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between São Paulo and Tokyo change during the year?: No. The gap stays at 12h all year.
When is the best time to call Tokyo from São Paulo?: There is no overlap between standard working days, so one side has to call early or late.