Although you already have a number of answers, still I want to provide another. I've been using Dvorak* for over a decade now, and I love it.
Mind you, I never claimed to be a particularly fast typist on any layout, although I have been touch typing for several decades, and on that note I am just as productive on Dvorak as on qwerty -- but at far lesser expense. That is to say, don't switch for the (mythical?) increased typing speed, switch for the ~30%(!) reduction in finger movement and pleasant "rolling" motions you gain.
True, it's not easy to share computers, be it you using somebody else's machine or somebody else using your machine. The latter can easily be addressed by quick layout changes (again, a pain to get right on Windows but a breeze on Linux), while I find that the former doesn't really bother me so much -- curiously, when I can't touch type (such as on my phone), I am hopelessly slow on Dvorak but quite efficient hunting-and-pecking on qwerty (possibly because I retain training from before touch typing?). The most glaring downside is the situations where keys and shortcuts are clearly laid out for qwerty and won't allow you to remap them (case in point: WASD in games); in reality most shortcuts are easy enough to use regardless of layout (side note: I've always been using Ctrl/Shift+Insert/Delete for cut/copy/paste, so the locations of X, C, and V don't affect me -- but modern keyboards with misplaced or missing Insert keys do).
To answer you question: I very specifically switched during the week before New Year's eve, when I could be reasonably sure that things at the office were slow enough to allow me to struggle through an unaccustomed layout. Honestly, the first days were atrocious, but within a week (so ~35 hrs) I had internalized the layout to a reasonable degree, and within a very few weeks (3? I don't really remember) I was up to my usual typing speed.
* Specifically, the Norwegian variant of Dvorak, because I need some localized keys. This has been a challenge, but a surmountable one, back on Windows (along with changing the keyboard layout for the Windows login screen, which truly defined the pinnacle of obscurity) -- on Linux it is dead simple to set up and just works.
Mind you, I never claimed to be a particularly fast typist on any layout, although I have been touch typing for several decades, and on that note I am just as productive on Dvorak as on qwerty -- but at far lesser expense. That is to say, don't switch for the (mythical?) increased typing speed, switch for the ~30%(!) reduction in finger movement and pleasant "rolling" motions you gain.
True, it's not easy to share computers, be it you using somebody else's machine or somebody else using your machine. The latter can easily be addressed by quick layout changes (again, a pain to get right on Windows but a breeze on Linux), while I find that the former doesn't really bother me so much -- curiously, when I can't touch type (such as on my phone), I am hopelessly slow on Dvorak but quite efficient hunting-and-pecking on qwerty (possibly because I retain training from before touch typing?). The most glaring downside is the situations where keys and shortcuts are clearly laid out for qwerty and won't allow you to remap them (case in point: WASD in games); in reality most shortcuts are easy enough to use regardless of layout (side note: I've always been using Ctrl/Shift+Insert/Delete for cut/copy/paste, so the locations of X, C, and V don't affect me -- but modern keyboards with misplaced or missing Insert keys do).
To answer you question: I very specifically switched during the week before New Year's eve, when I could be reasonably sure that things at the office were slow enough to allow me to struggle through an unaccustomed layout. Honestly, the first days were atrocious, but within a week (so ~35 hrs) I had internalized the layout to a reasonable degree, and within a very few weeks (3? I don't really remember) I was up to my usual typing speed.
Bonus: here, have a go and try for yourself: http://gigliwood.com/abcd/lessons/ (no affiliation)
* Specifically, the Norwegian variant of Dvorak, because I need some localized keys. This has been a challenge, but a surmountable one, back on Windows (along with changing the keyboard layout for the Windows login screen, which truly defined the pinnacle of obscurity) -- on Linux it is dead simple to set up and just works.