What Is Implantation Bleeding How Long Does The Implantation Bleeding Last?

How long does the implantation bleeding last? - what is implantation bleeding

My girlfriend took the Plan B pill, and a week later had time. Their time lasted only 3 days. Perhaps it was a normal period or was implantation bleeding. How long should implantation bleeding last? Do you have a real deadline, which was only 3 days because of the pill or is it implantation bleeding? What do you think?