The mother needs to shed the afterbirth within 24 hours of kidding. Most of the time, they shed it within hours. If there is some still hanging after 24 hours, you can try to "gently" pull it out. Some times the "gravity" has not taken effect and a gentle pull will remove the last of it. If you gently pull and it starts to come out without any "resistance", everything is ok. If not, you can give the doe some Oxytocin. This will help the doe shed the afterbirth and help bring in her milk.
We use to think that after a doe shed her afterbirth, she will not have any more kids at that time. We had a doe give birth to a single and then shed her afterbirth four hours later. We expected twins and she still looked like she had another kid but there was no more labor. We checked on her eight hours later and nothing was happening so we assumed she was through. The next morning we found another kid dead in the pen. It was the same size and looked healthy. The vet said it can occur and the kid born after a doe loses her afterbirth is normally born dead.