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

No. The gap stays at 1h all year.

When is the best time to call Tokyo from Shanghai?

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

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

Shanghai

China

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Tokyo

Japan

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

City	Time zone	UTC offset
Shanghai · China	Asia/Shanghai	UTC+8
Tokyo · Japan	Asia/Tokyo	UTC+9

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