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

Yes. Because of daylight saving time the gap moves between +4h and +5h.

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

Between 14:00 and 17:00 in Madrid, which is 09:00 to 12:00 in São Paulo.

Madrid is 5h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +4h and +5h during the year.

Madrid

Spain

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São Paulo

Brazil

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A 9-to-5 day in each city overlaps for 3h. That is 14:00–17:00 in Madrid, which is 09:00–12:00 in São Paulo.

City	Time zone	UTC offset
Madrid · Spain	Europe/Madrid	UTC+2
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Madrid and São Paulo?: Madrid is 5h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +4h and +5h during the year.
Does the time difference between Madrid and São Paulo change during the year?: Yes. Because of daylight saving time the gap moves between +4h and +5h.
When is the best time to call São Paulo from Madrid?: Between 14:00 and 17:00 in Madrid, which is 09:00 to 12:00 in São Paulo.