Sorry, can't give you a timeline. Molluscum can be contagious, but often isn't (despite being termed 'contagiosum.' It occurs quite often in kids, usually on their chest, without anyone in the vicinity having it. So the fact that your girlfriend has it does not necessarily mean that she's been playing around, if that's your concern. As to where they did come from, it's often impossible to say.
Best.
Dr. Rockoff