Implantation cramps when pregnant last from 1 to 3 days and having implantation cramps is also one of the first signs that you're pregnant and the implantation cramps usually happen after 8 to 12 days after ovulation happens when your fertilized egg makes it's way down your fallopian tube and then implants itself into your uterine lining.
The implantation cramps are usually mild and you should stop cramping after 3 days.