How much time does it take for women to start menstruating again?

It depends on how much she is breastfeeding and how well nourished she is.

A woman who is breastfeeding on demand, never having a gap of more than 6 hours throughout the day and night and not using a dummy or any other artificial means of withholding a feed is unlikely to start ovulating (and therefore menstruating) again before 6 months. It's sometimes used as a form of contraception, called lactational amenorrhoea but it's a risky one to use, there are certain conditions you have to follow.

Some research done in Keneba (a village in the Gambia, West Africa) showed that supplementing lactating women's diets made no difference to their breastmilk output, as measured by the babies' input, (which had been the aim of the researchers), but the mothers' prolactin levels went down and some of them ovulated. It was not clear if the supplement directly reduced the prolactin levels, or whether it simply increased the speed of milk flow, so reducing suckling time and breast stimulation and thence reducing prolactin. I can't find an online reference to the research - I got it from The Politics of Breastfeeding by Gabrielle Palmer.

I just reread your question, and realised you also wanted us to include our personal experiences. I have always started again at about 8 months - once my children are well established on solids and feeding less from me.

I breastfed and didn't get my period back until my daughter was almost a year. Yet another awesome reason to nurse. :-)

I didnt breast feed but, but had emergency c-section and bled for 6 weeks then 2 weeks later had a period.