Depending on the size, color, and location of the tattoo, it takes about 6-8 sessions total to sufficiently reduce the appearance of the tattoo but not necessarily completely remove it. Each session only takes about 10-20 minutes, and theres no downtime involved.
Its recommended that patients wait 6 weeks between each treatment for several reasons. The first is that after a laser treatment, the body starts drawing the old ink out of the area and continues to do so for about 5-6 weeks. That means having another treatment before those 6 weeks are up will be ineffective, and therefore unnecessary. The second reason is that the skin needs enough time to properly heal between sessions.
Another factor that determines how many sessions are needed is the patients skin tone. Because laser light is absorbed by pigment in the skin, tattoo pigment can be targeted much easier on lighter skin.