Does the time difference between Dubai and Madrid change during the year?

Yes. Because of daylight saving time the gap moves between +2h and +3h.

When is the best time to call Madrid from Dubai?

Between 11:00 and 17:00 in Dubai, which is 09:00 to 15:00 in Madrid.

Dubai is 2h ahead of Madrid. This gap is not fixed: daylight saving time moves it between +2h and +3h during the year.

Dubai

United Arab Emirates

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Madrid

Spain

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A 9-to-5 day in each city overlaps for 6h. That is 11:00–17:00 in Dubai, which is 09:00–15:00 in Madrid.

City	Time zone	UTC offset
Dubai · United Arab Emirates	Asia/Dubai	UTC+4
Madrid · Spain	Europe/Madrid	UTC+2

What is the time difference between Dubai and Madrid?: Dubai is 2h ahead of Madrid. This gap is not fixed: daylight saving time moves it between +2h and +3h during the year.
Does the time difference between Dubai and Madrid change during the year?: Yes. Because of daylight saving time the gap moves between +2h and +3h.
When is the best time to call Madrid from Dubai?: Between 11:00 and 17:00 in Dubai, which is 09:00 to 15:00 in Madrid.