Most Turkish offices work 09:00 to 18:00, Monday to Friday, with an hour for lunch around 12:30. The weekend is Saturday and Sunday, as in Europe, not Friday and Saturday as in much of the Middle East.
Banks generally open 09:00 to 17:00 on weekdays and close at weekends. Government offices tend to run 08:30 to 17:30 and can close earlier in summer.
Retail keeps much longer hours. Shopping centres commonly open 10:00 to 22:00 seven days a week. The Grand Bazaar in Istanbul runs roughly 09:00 to 19:00 and closes on Sundays, which surprises a lot of visitors.
Restaurants serve late, and in coastal resorts in summer the evening does not really begin until after 21:00.
From western Europe the overlap is nearly total: the whole Turkish working day falls inside yours. From South and South-East Asia the Turkish day starts in your early afternoon and runs into your evening.
From North America the window is narrow. Turkish close of business at 18:00 is 11:00 in New York and 08:00 in Los Angeles, so an early call is the only reliable option.
Monday to Friday, with Saturday and Sunday as the weekend.
Most are, including shopping centres and supermarkets. The Grand Bazaar is a notable exception and closes on Sundays.
Usually 17:00 on weekdays, and they do not open at weekends.