AF Not here!! When does the implantation happen

I had a question. I was supposed to start my AF today. But i didn't get it today. On the 5th i spotting a brown color. On the 6th only when i wiped it was a brown color. As of today no spotting over the night just when I wiped it was a brown color. I was wondering is it possible that it was implantation? Oh and my fertility week was the 19-26 I think