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

Yes. Because of daylight saving time the gap moves between +7h and +8h.

When is the best time to call Toronto from Istanbul?

Between 16:00 and 17:00 in Istanbul, which is 09:00 to 10:00 in Toronto.

Istanbul is 7h ahead of Toronto. This gap is not fixed: daylight saving time moves it between +7h and +8h during the year.

Istanbul

Türkiye

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Toronto

Canada

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A 9-to-5 day in each city overlaps for 1h. That is 16:00–17:00 in Istanbul, which is 09:00–10:00 in Toronto.

City	Time zone	UTC offset
Istanbul · Türkiye	Europe/Istanbul	UTC+3
Toronto · Canada	America/Toronto	UTC−4

What is the time difference between Istanbul and Toronto?: Istanbul is 7h ahead of Toronto. This gap is not fixed: daylight saving time moves it between +7h and +8h during the year.
Does the time difference between Istanbul and Toronto change during the year?: Yes. Because of daylight saving time the gap moves between +7h and +8h.
When is the best time to call Toronto from Istanbul?: Between 16:00 and 17:00 in Istanbul, which is 09:00 to 10:00 in Toronto.