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

No. The gap stays at 1h all year.

When is the best time to call Toronto from Chicago?

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

Chicago is 1h behind Toronto. This gap is the same all year — neither city shifts its clocks relative to the other.

Chicago

United States

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Toronto

Canada

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A 9-to-5 day in each city overlaps for 7h. That is 09:00–16:00 in Chicago, which is 10:00–17:00 in Toronto.

City	Time zone	UTC offset
Chicago · United States	America/Chicago	UTC−5
Toronto · Canada	America/Toronto	UTC−4

What is the time difference between Chicago and Toronto?: Chicago is 1h behind Toronto. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Chicago and Toronto change during the year?: No. The gap stays at 1h all year.
When is the best time to call Toronto from Chicago?: Between 09:00 and 16:00 in Chicago, which is 10:00 to 17:00 in Toronto.