Between 2015 and 2018, I had about fifteen laser treatments. At first, they were spaced four weeks apart, then the spacing was lengthened to six weeks. After the first twelve sessions, I went for three "touch up" about six months apart.
I had a good amount of gray/white hair mixed int with my brown hair and lasers are ineffective on gray/white hair. Nonetheless, after the first two treatments, over 90% of the dark hair was gone. In fact, about two weeks after the first treatment, I had a "Holy &*%$" moment when I realized all the dark hair on the sides and top was completely gone and only two smallish patches remained on the back. I was pretty much shadow-free after just a couple sessions.
It's been over five years since my last session and a little dark hair has returned, mostly at the back of my head. It really isn't noticeable as a shadow. I shave about every three days because the gray/white continue to grow.
Overall, I am happy with the results.