Counter anecdote; I switched to split ortho a couple weeks ago and it didn't take much more than a week of consistently using only the new keyboard to get back up to normal speeds. The ortho seems to have made it much easier for me to touch type, as a result of which I now make fewer errors and generally barely ever consciously think about the actual action of typing.

Took me like 3 or 4 days to get up to my normal speed of a bit over 100wpm.

This was also going from 60% to my first split/ortho.

Took me another couple of days to get used to chording and these days I use a 36 key split board.

So your mileage may vary, but it's definitely not going to take you months typically.