I'm wondering how long will it take for my impacted tooth to come down?

Depends: If the tooth is not vertical or is being blocked by an adjacent tooth, it may never come down. Only a local dentist with a radiograph of the tooth can give you a clear understanding of your condition.

See a dentist: Wisdom teeth usually appear between the ages of 16 and 25. However, sometimes they appear many years later. If you are experiencing pain and it does not go away or if you find it difficult to open your mouth, you should see a dentist for evaluation, x-ray and wisdom teeth removal.

Impacted: If it's impacted it is, by definition, blocked from erupting. Do not depend on spontaneous eruption, it won't happen. If you have an impacted wisdom tooth it teeth, see an Oral Surgeon. If it is any other tooth, see an Orthodontist.