How long after implantation will a hpt detect hcg?

AF is due tomorrow, I've had zero pms symptoms and had pain on my left side (which is the side I ovulated on this month) with some brownish spotting today. I have a short cycle and am only 9dpo. I am praying this was implantation bleeding/cramps. I am finding contradictory information online, so was curious as to others experience or knowledge... How long after implantation (on average) will a hpt detect hcg? Thanks in advance!