I thought it would take a long time all at once, but maybe because it was just three 15-minute sessions, it felt like it finished faster than I expected haha. When I had this done elsewhere before, they made me bite down with my molars, sealed it like a plaster cast, and I couldn't even swallow my saliva... having the device in my mouth was really uncomfortable ㅠ. But this time, they proceeded without that process, so I felt much more comfortable. For now, I plan to just observe it, and if the color darkens again later, I intend to go back for another session haha.