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

No. The gap stays at 4h all year.

When is the best time to call Lagos from Karachi?

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

Karachi is 4h ahead of Lagos. This gap is the same all year — neither city shifts its clocks relative to the other.

Karachi

Pakistan

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Lagos

Nigeria

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

City	Time zone	UTC offset
Karachi · Pakistan	Asia/Karachi	UTC+5
Lagos · Nigeria	Africa/Lagos	UTC+1

What is the time difference between Karachi and Lagos?: Karachi is 4h ahead of Lagos. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Karachi and Lagos change during the year?: No. The gap stays at 4h all year.
When is the best time to call Lagos from Karachi?: Between 13:00 and 17:00 in Karachi, which is 09:00 to 13:00 in Lagos.