How long will it take?
“How long will it take?” might be the wrong question.
How long will it take to write a book? It depends. Some excellent books were written in weeks, and some took fifteen years.
How long will it take to learn to play the guitar? It depends. Can you practice for fourteen hours a day? If so, probably not that long.
Maybe the question is actually: how much time do you want to work on it today? Also: how important is it to you that you eventually succeed?