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

No. The gap stays at 11h all year.

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

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

Beijing is 11h ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.

Beijing

China

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São Paulo

Brazil

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

City	Time zone	UTC offset
Beijing · China	Asia/Shanghai	UTC+8
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Beijing and São Paulo?: Beijing is 11h 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 Beijing and São Paulo change during the year?: No. The gap stays at 11h all year.
When is the best time to call São Paulo from Beijing?: There is no overlap between standard working days, so one side has to call early or late.