Years is a little bit too much yes. I also did a full switch after 1 month of "klavaro" [1] training, but I think it took me nearly one year to be "fully" adapted. By "fully" I mean not thinking anymore about QWERTZ: not for french, nor for english, nor for coding and for beating my previous QWERTZ capabilities.
Interesting. I don't really remember how long that took me, it's been some eight years now since I switched. I used ktouch to practise, which has lessons for neo2 and, apparently, BÉPO.
[1] http://klavaro.sourceforge.net/en/index.html