It clicked after a year of practice, the change was quick and noticeable. I started learning after moving to France and it helps a great deal even though at work it's English. Not sure how long it would take if I was learning it elsewhere.
It definitely takes longer if you don't live in an environment where it's spoken. Before I moved to NL from the US, I did duolingo every day for 3 months (from the time I accepted the offer to moving) and by the time I got on the plane, I had moved from the beginner module to the intermediate one. After landing and getting settled, I ventured out to really test my skills at the local supermarket and I was completely and utterly useless. Perhaps the only thing I could recognize was the total at the end that I needed to pay.
We take for granted regional dialects when speaking our own language and in some languages, dialects can be a huge component of the language. Being able to just go outside and sit on a bench and listen to people speak in the language you want to learn is a huge advantage. Every day, you will passively pick up some words from the context of passers-by. You'll also start to subconsciously figure out what words are "common" in a different way that the lists of "1000 most common words in X langauge" can convey. You also learn how to put them together in context and how some words travel together within a certain context.
If I was tasked with learning a language abroad, I would spend 2-4 hours a day consuming native content and make it a priority to speak with a coach online 1-2 times a week, trying to work my way up to holding a conversation for an hour straight.
After living here for almost 2 years now, I can just barely get to 1 hour when speaking to my boss (super grateful btw!) but I'm really drained mentally by the end of it. With each meeting it gets easier though and now I can somewhat even make out the local dialect. Learning a language is a numbers game and the reason we often attribute superior language learning skills to kids is simply due to the fact that they have so much free time to listen, absorb, speak, and make mistakes without people judging them because they're kids. I'm fully convinced that adults can learn just as fast or faster, but our own egos often get in the way to putting in the work to learn.
