How long does it take to learn an instrument?

Depends on the instrument and your willingness to learn.

Some people are very talented and can pick it up quickly, while others will never become proficient. 

🥴

By ear? 

It depends. 

The average can pick up on notes on the 1st day.

That depends on the point in your development you would consider that you've learned (because you probably could go on learning past that point).  In other words, what criteria do you use for judging that you've learned the instrument?  It also depends on how much talent you have for playing that instrument and for music in general, and especially, on how much you practice.  Also, whether or not you have a teacher and how good the teacher is.  

Six point two.