The average student that trains diligently, at least three times a week, can potentially become a black belt in about 3 1/2 to 5 years. This large window of time is based on individual skill and  natural ability. I have never met a black belt, no matter how naturally skill he or she is, that actually has the skills of a true black belt, without at least 3 1/2 to 5 years of consistent training. Try as you may, there is no substitute for time to balance the skills you acquire.