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

No. The gap stays at 10h all year.

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

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

Jakarta is 10h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.

Jakarta

Indonesia

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São Paulo

Brazil

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

City	Time zone	UTC offset
Jakarta · Indonesia	Asia/Jakarta	UTC+7
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Jakarta and São Paulo?: Jakarta is 10h 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 Jakarta and São Paulo change during the year?: No. The gap stays at 10h all year.
When is the best time to call São Paulo from Jakarta?: There is no overlap between standard working days, so one side has to call early or late.