I think that learning piano is not necessarily a difficult instrument, because difficulty is a changing concept. How? In an amusement park, is going down a scary slide difficult or fun? And why it is that they create more and more white knuckle rides? Because we love them.
Piano, I would argue is the same.
It doesn’t take long at all to learn it, as long as you think it is fun.
What is a few scales? A fingering on the correct notes? A few improvisations over a gentle bass line? What is understanding what is on the paper? How to play a children song? How to pluck a few chords? Is it time? Or is it the feeling, the irrepressible feeling that you can do it, that right then and there, once you got it, you could swear you are flying?!!! And, once you got those concepts, your curious mind is looking for a new challenge, and you find one, and that one too is a little mountain to climb, and you sweat sometimes, and you curse a little, but once you can proudly plant your flag on top of that concept, you are a different person.
How long does it take to learn the piano? Is that the question?
Here is another challenge: How long does it take to have fun??