First, I don't micromanage my cities.
After that it depends if I am at war or not. If I am not at war, the turn lasts as long as it takes me to get through the tech window (if I researched something), my build windows, and to order my workers.
If I am at war, I will spend more time planning that turn's worth of manuvers. I will look at everything from health of units, proximity of enemy units, reinforcement locations, and available movements. A long turn for me might take 10 minutes.