How long does laser treatment for vitiligo work?

Depends. Vitiligo is an autoimmune disease - your immune cells attack pigment cells in your skin. Laser treatments can suppress the autoimmune response, allowing the pigment cells and skin color to come back. Unfortunately it can take many treatments to see results. Maintenance laser treatments are often needed or the vitiligo is likely to come back.
Depends. Your dermatologist can best explain this answer to you and it is extremely difficult to determine every single person's response to laser therapy. All vitiligo patients respond differently. You might have great results initially or it might take time to get the benefit you are looking for. Main thing is to stay compliant with the treatments.

Related Questions

How does laser treatment for vitiligo work?

UVB light. Laser therapy is an effective treatment for vitiligo, although impractical for the treatment of widespread or large lesions, since it is focused on small, targeted areas. Combination with topical therapies can be helpful. The laser emits ultraviolet light which somehow interferes with the autoimmune process that may be destroying the melanocytes (which give us our skin pigmentation).
Decreases the contra. Laser treatment for vitiligo decreases the surrounding normal pigment to decrease the contrast of having no pigment in the vitiligo with normal undamanged skin.

I have vitiligo patches on my lips, underarms, thighs, palms, legs. I'm undergoing Excimer laser treatment. It's getting worse than being healed. Pls help?

Talk to doctor. This is something you need to discuss with the treating doctor. If it is getting worse, I don't see any reason to continue with it but you still need to discuss this with him/her.