Does the time difference between Istanbul and Moscow change during the year?

No. Both cities keep the same local time all year.

When is the best time to call Moscow from Istanbul?

Between 09:00 and 17:00 in Istanbul, which is 09:00 to 17:00 in Moscow.

Istanbul and Moscow are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.

Istanbul

Türkiye

--:--:--

Moscow

Russia

--:--:--

A 9-to-5 day in each city overlaps for 8h. That is 09:00–17:00 in Istanbul, which is 09:00–17:00 in Moscow.

City	Time zone	UTC offset
Istanbul · Türkiye	Europe/Istanbul	UTC+3
Moscow · Russia	Europe/Moscow	UTC+3

What is the time difference between Istanbul and Moscow?: Istanbul and Moscow are on the same local time. This gap is the same all year — neither city shifts its clocks relative to the other.
Does the time difference between Istanbul and Moscow change during the year?: No. Both cities keep the same local time all year.
When is the best time to call Moscow from Istanbul?: Between 09:00 and 17:00 in Istanbul, which is 09:00 to 17:00 in Moscow.