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

Yes. Because of daylight saving time the gap moves between −6h and −5h.

When is the best time to call Zurich from Toronto?

Between 09:00 and 11:00 in Toronto, which is 15:00 to 17:00 in Zurich.

Toronto is 6h behind Zurich. This gap is not fixed: daylight saving time moves it between −6h and −5h during the year.

Toronto

Canada

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Zurich

Switzerland

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A 9-to-5 day in each city overlaps for 2h. That is 09:00–11:00 in Toronto, which is 15:00–17:00 in Zurich.

City	Time zone	UTC offset
Toronto · Canada	America/Toronto	UTC−4
Zurich · Switzerland	Europe/Zurich	UTC+2

What is the time difference between Toronto and Zurich?: Toronto is 6h behind Zurich. This gap is not fixed: daylight saving time moves it between −6h and −5h during the year.
Does the time difference between Toronto and Zurich change during the year?: Yes. Because of daylight saving time the gap moves between −6h and −5h.
When is the best time to call Zurich from Toronto?: Between 09:00 and 11:00 in Toronto, which is 15:00 to 17:00 in Zurich.