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

Yes. Because of daylight saving time the gap moves between +3h and +4h.

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

Between 13:00 and 17:00 in Dublin, which is 09:00 to 13:00 in São Paulo.

Dublin is 4h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +3h and +4h during the year.

Dublin

Ireland

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São Paulo

Brazil

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A 9-to-5 day in each city overlaps for 4h. That is 13:00–17:00 in Dublin, which is 09:00–13:00 in São Paulo.

City	Time zone	UTC offset
Dublin · Ireland	Europe/Dublin	UTC+1
São Paulo · Brazil	America/Sao_Paulo	UTC−3

What is the time difference between Dublin and São Paulo?: Dublin is 4h ahead of São Paulo. This gap is not fixed: daylight saving time moves it between +3h and +4h during the year.
Does the time difference between Dublin and São Paulo change during the year?: Yes. Because of daylight saving time the gap moves between +3h and +4h.
When is the best time to call São Paulo from Dublin?: Between 13:00 and 17:00 in Dublin, which is 09:00 to 13:00 in São Paulo.