Question for DPO


Hey ladies, please excuse the silly question. I have a 30 day cycle and ovulated on CD16. I'd read somewhere that implantation can happen anywhere from 6dpo to 12dpo but 12dpo would be 2 days before AF is due, so if implantation doesn't happen until the 12th day, how long after a missed period would I have to wait to take a test? My AF is due on the 21st. Please help!

Thank you and baby dust to all!