Most whitening appointments take around an hour, perhaps two hours to complete, depending on how long the formula needs to remain on the teeth. Your dentist will prep your mouth, apply the whitener, and allow it to work, before cleaning you up and sending you on your way.
The results of whitening are instant, and you will often leave the appointment with your teeth looking two or three shades lighter than what you came in with. The treatment is painless, although some patients experience tooth sensitivity with warm or cold foods and drinks. This is temporary and will pass after a short period, usually a few days.