Does the time difference between Dublin and Karachi change during the year?

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

When is the best time to call Karachi from Dublin?

Between 09:00 and 13:00 in Dublin, which is 13:00 to 17:00 in Karachi.

Dublin is 4h behind Karachi. This gap is not fixed: daylight saving time moves it between −5h and −4h during the year.

Dublin

Ireland

--:--:--

Karachi

Pakistan

--:--:--

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

City	Time zone	UTC offset
Dublin · Ireland	Europe/Dublin	UTC+1
Karachi · Pakistan	Asia/Karachi	UTC+5

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