How To Recognize Implantation Bleeding?

I stopped taking birth control July 26th to try and conceive after my next regular period. Had my birth control induced period on July 30th. On August 6th had intercourse and the condom broke (like I said we were trying to be careful until I had a regular period to chart my cycle). On August 24th had light spotting but not period. I am wondering if implantation bleeding possible 18 days after sex? All the information I read says sperm can live at most 5 days and implantation usually happens 6-10 days after that so is 18 days too long for implantation to occur?