I think it takes most folks years to teach themselves to bow competently. But, a good teacher can send you down the right path in a few lessons, maybe as little as two, with a follow up later. By good teacher, though, I mean someone who can actually explain and demonstrate the mechanics of how to use the bow to best effect. There are lots of great acro players who haven't a clue how to explain bowing to a new student, so don't except responses, like, "just keep hacking at the string using all of the bow length and it will get better." That's probably true, but it takes a long time.