Mine lasted two days, it was only noticeable when I wiped. I think it happened at about 5weeks but that does seem late doesn't it?!
Just looked at babycentre.co.uk and this is what they say "Implantation bleeding or cramping. About eight days after ovulation, you may experience implantation spotting, a slight staining of a pink or brown colour, as well as some cramping. This is caused by the egg burrowing into the endometrial lining. You might also see some spotting around the time you expect your period. "