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

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

When is the best time to call Zurich from Tokyo?

Between 16:00 and 17:00 in Tokyo, which is 09:00 to 10:00 in Zurich.

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

Tokyo

Japan

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Zurich

Switzerland

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

City	Time zone	UTC offset
Tokyo · Japan	Asia/Tokyo	UTC+9
Zurich · Switzerland	Europe/Zurich	UTC+2

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