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

Yes. Because of daylight saving time the gap moves between −1h and 0.

When is the best time to call Cairo from Berlin?

Between 09:00 and 16:00 in Berlin, which is 10:00 to 17:00 in Cairo.

Berlin is 1h behind Cairo. This gap is not fixed: daylight saving time moves it between −1h and 0 during the year.

Berlin

Germany

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Cairo

Egypt

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

City	Time zone	UTC offset
Berlin · Germany	Europe/Berlin	UTC+2
Cairo · Egypt	Africa/Cairo	UTC+3

What is the time difference between Berlin and Cairo?: Berlin is 1h behind Cairo. This gap is not fixed: daylight saving time moves it between −1h and 0 during the year.
Does the time difference between Berlin and Cairo change during the year?: Yes. Because of daylight saving time the gap moves between −1h and 0.
When is the best time to call Cairo from Berlin?: Between 09:00 and 16:00 in Berlin, which is 10:00 to 17:00 in Cairo.