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

Yes. Because of daylight saving time the gap moves between +4h and +5h.

When is the best time to call Cairo from Bangkok?

Between 13:00 and 17:00 in Bangkok, which is 09:00 to 13:00 in Cairo.

Bangkok is 4h ahead of Cairo. This gap is not fixed: daylight saving time moves it between +4h and +5h during the year.

Bangkok

Thailand

--:--:--

Cairo

Egypt

--:--:--

A 9-to-5 day in each city overlaps for 4h. That is 13:00–17:00 in Bangkok, which is 09:00–13:00 in Cairo.

City	Time zone	UTC offset
Bangkok · Thailand	Asia/Bangkok	UTC+7
Cairo · Egypt	Africa/Cairo	UTC+3

What is the time difference between Bangkok and Cairo?: Bangkok is 4h ahead of Cairo. This gap is not fixed: daylight saving time moves it between +4h and +5h during the year.
Does the time difference between Bangkok and Cairo change during the year?: Yes. Because of daylight saving time the gap moves between +4h and +5h.
When is the best time to call Cairo from Bangkok?: Between 13:00 and 17:00 in Bangkok, which is 09:00 to 13:00 in Cairo.