Pretty much immediately.
I don't really even get what the big deal is, but especially for those who were losing their hair in the first place.
If your pate was showing (the top of your head) then you were bald already, who gives a rat's ass about the hair on the sides and back?!? That doesn't count as "having hair", IMO.
So it's not a major change anyway.
I have no problem being sly; and I have to deal with ugly hair transplant scars all over the back of my noggin. (and some at the top front, but there, mostly, just dark circles where the hair follicles are showing, even after being shaved fresh) They're annoying, but if I didn't have those problems, I wouldn't even think twice about being sly.
If you ain't got hair on TOP, then you ain't got hair anyway - get over it.
So for those of you who can't get used to the idea of a smooth dome, hey - it could be a lot worse. You could be me.