"As needed" I would say around the 2 year mark, but with a bit of a blip to think about it.
But I could do this at the 6 month mark, just not accurately.. I would still be messing up letters at a ~1% rate, let's say.
Dvorak with vim isn't that bad. HJKL is in a row on QWERTY, but Dvorak at least has JK together, and H to the left of L.
CUA keybindings like Ctrl X, Ctrl C, Ctrl P can be a pain with Dvorak. (I also don't think shortcuts like Ctrl+Insert, Shift+Insert are widely supported across OSs, nor USB HID's copy and paste keys).
Other than that, it's just about remembering the shortcut by the letters, not by the position of the keys.
That being said, this year I decided enough was enough, and I worked to relearn QWERTY. Initially it was really hard, but after a few weeks, I managed to get to a comfortable speed. Here is an image showing my QWERTY averages since March of this year: https://i.imgur.com/RESfuFS.png My average has plateau'd around 80wpm, which is a great speed, and I managed to do that without sacrificing my Dvorak speed, which sits at 125wpm. Finally, to throw a wrench into it, I also decided to learn Colemak this year... and with enough practice I've gotten to the point where I can switch between the three without any issue.
I hardly ever type on a Qwerty keyboard though.