Does the time difference between Beijing and Berlin change during the year?

Yes. Because of daylight saving time the gap moves between +6h and +7h.

When is the best time to call Berlin from Beijing?

Between 15:00 and 17:00 in Beijing, which is 09:00 to 11:00 in Berlin.

Beijing is 6h ahead of Berlin. This gap is not fixed: daylight saving time moves it between +6h and +7h during the year.

Beijing

China

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Berlin

Germany

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

City	Time zone	UTC offset
Beijing · China	Asia/Shanghai	UTC+8
Berlin · Germany	Europe/Berlin	UTC+2

What is the time difference between Beijing and Berlin?: Beijing is 6h ahead of Berlin. This gap is not fixed: daylight saving time moves it between +6h and +7h during the year.
Does the time difference between Beijing and Berlin change during the year?: Yes. Because of daylight saving time the gap moves between +6h and +7h.
When is the best time to call Berlin from Beijing?: Between 15:00 and 17:00 in Beijing, which is 09:00 to 11:00 in Berlin.