wow, it took me 3 weeks to get basic proficiency, but really slow. 6 months to parity with qwerty, about a year before I was truly comfortable with it. probably about 2 years before I was completely fluent with both, and 5 years before my brain could map my own personal keyboards with dvorak and default to qwerty in all other cases with nearly zero mistakes. These days (20 years on) I have no problem, running, say virt-manager, which does not respect the linux key remapping, and typing in non-dvorak even on my own machine in a context-dependent fashion.
I had the experience of changing to colemak and then spending maybe two months not practicing deliberately. Progress was slow. But then, I started practicing every day and I was back to my qwerty speeds within a few weeks. The incidental practice you get from typing in your everyday life isn't enough to quickly get learn a new layout, unfortunately.
