I judge by the female and how she looks. Could be right away, could be a few weeks later. Some slow breeders I allow open while they have kits, as typically they won't breed back for me and only produce 1 litter a year.
As for retiring it depends. I don't mind if a female only gives me one litter a year--so I don't retire for lack of production. If she looks worn out, looks like she isn't handling raising the kits as good as she used to, etc I will pull her and retire her. If she starts having complications, i'll retire her. It all depends on the female in question.