This does take about a hour and half for the whole process,
under the zoom light for 3-4 15 min sessions, I believe I was under 4 times and it took a hour - they do their best to protect your gums but I noticed a small buring sensation on 2nds and 4the sessions in different areas. No real tooth sensitivity until after I got home!
My gums stopped hurting once they took the light off of them, and rubbed oil on them. They told me to take ibprofin for releif of tooth sensitivity, the 1st day only I would have sharp stabbing pains in my teeth, very painful, but very occassional, not constant, they would come and go.
Today is my 2nd day and I have not noticed anything other than my very white smile! It did work very well and my teeth are very white, They fitted me for a take home tray for maintance I will pick up in a few days from now.
I am very happy with the overall results, my teeth are whiter than my teenage daughters now, I am 40 - It really did refreshen my smile! Very happy and would do it again.