You can probably get pretty far self teaching and practicing. I am fully self taught but I’ve been designing for a long time. I have a large list of clients behind me and multiple agency experiences.

I’d read everything I can, learn the tools and practice a lot. Goal should be to get paying work in the field as soon as possible. Look for UI/UX designer position once you feel comfortable and have a portfolio. Preferably take on a few freelance clients and make something you can show off that you got paid for.

There’s no time frame I can give - all depends on your motivation, effort and ability to learn and move fast.

All I can say is that no one ever becomes a good designer - it’s always a work in progress and you’ll constantly look back at your previous work wondering how it was so bad.