8 weeks. I'm looking for it this time around.
i didn't notice mine till I wanna say 28w or so. if not a little later
the dark line has always been there it just wasn't so dark so you couldn't see it.
I had it before I got pregnant but most people get it I'm not sure exactly when tho
at around 18 I believe it's super dark and goes from the top of my hooha to in between my breasts