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

No. The gap stays at 8h 30m all year.

When is the best time to call São Paulo from New Delhi?

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

New Delhi is 8h 30m ahead of São Paulo. This gap is the same all year — neither city shifts its clocks relative to the other.

New Delhi

India

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São Paulo

Brazil

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

City	Time zone	UTC offset
New Delhi · India	Asia/Kolkata	UTC+5:30
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between New Delhi and São Paulo?: New Delhi is 8h 30m 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 New Delhi and São Paulo change during the year?: No. The gap stays at 8h 30m all year.
When is the best time to call São Paulo from New Delhi?: There is no overlap between standard working days, so one side has to call early or late.