If you experienced implantation bleeding before getting a BFP, 1. how long did it last and 2. how long before you got the BFP?

This is my first cycle post-BC and I'm on CD40 now. Last POAS from Sunday (1/13) was negative. Monday and Tuesday I experienced light cramping so I figured AF was on the way. Wednesday morning I woke up with light spotting. It was a dark brown and went away after peeing. I wore a panty liner and had only slight spotting throughout the day. Same thing today now. It hasn't gotten any heavier and it isn't AF red either. I'm wondering if it could be late ovulation implantation bleeding?