Istanbul is on Turkish time, UTC+3, like the rest of the country. What changes from city to city is the daylight.
Turkey keeps one time zone across roughly 1,600 km, so the clock in Istanbul matches Istanbul exactly while the sun rises at a different moment. The figures above are calculated for Istanbul's own coordinates and update as the date changes.
Istanbul is the only major city in the world built across two continents, with the Bosphorus running between its European and Asian halves. It is Turkey's largest city by a wide margin and its commercial centre, though Ankara is the capital.
Because Istanbul sits at Turkey's western edge, it gets the country's latest sunrises. In late December the sun does not come up until after 08:20 local time, which is unusually late for a city at this latitude and is a direct consequence of the whole country running on UTC+3.
Istanbul is in the Marmara region of Turkey.