Does the time difference between Mumbai and Zurich change during the year?

Yes. Because of daylight saving time the gap moves between +3h 30m and +4h 30m.

When is the best time to call Zurich from Mumbai?

Between 12:30 and 17:00 in Mumbai, which is 09:00 to 13:30 in Zurich.

Mumbai is 3h 30m ahead of Zurich. This gap is not fixed: daylight saving time moves it between +3h 30m and +4h 30m during the year.

Mumbai

India

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Zurich

Switzerland

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A 9-to-5 day in each city overlaps for 4h 30m. That is 12:30–17:00 in Mumbai, which is 09:00–13:30 in Zurich.

City	Time zone	UTC offset
Mumbai · India	Asia/Kolkata	UTC+5:30
Zurich · Switzerland	Europe/Zurich	UTC+2

What is the time difference between Mumbai and Zurich?: Mumbai is 3h 30m ahead of Zurich. This gap is not fixed: daylight saving time moves it between +3h 30m and +4h 30m during the year.
Does the time difference between Mumbai and Zurich change during the year?: Yes. Because of daylight saving time the gap moves between +3h 30m and +4h 30m.
When is the best time to call Zurich from Mumbai?: Between 12:30 and 17:00 in Mumbai, which is 09:00 to 13:30 in Zurich.