Many years later, this response has helped!! ** birthing right now*** I had to move the placenta with kitten up closer to her head, but she immediately started chewing on it. Thanks!Sometimes I find that showing the mother the afterbirth will entice her to cut the cord and eat it.
Keep us posted. As for how long to wait I have had kittens go a half hour to 45 minutes with it still attached and were fine.