How long does an appointment from a dentist take for just a cleaning of teeth?

How much? How much cleaning do you need? Are teeth straight and easily accessible? Do they have little or no tarter above or below the gums? Are they stained? So many other factors. Plan on about an hour to start. If there are extenuating circumstances, additional time (appointments) may need to be scheduled. In the grand scheme of things, it's time well spent.
At least an hour. It depends on the dental office and the health of your mouth. In my office we schedule a new patient examination for the exam, diagnosis and treatment plan and then the dental cleaning once we know the health of the mouth and what is needed. We schedule an hour for a routine adult dental hygiene visit. Many patients need more than this.