I lost a pregnancy that I got a positive POAS at like 8dpo. But I know I had sex the morning I ovulated, so everything went by the books on quickest timing. I only tested that early because I had really bad morning sickness. The line was faint, but there. I tested that morning with nothing and that afternoon I got a BFP. It was fun watching the line progression. I should also note that pregnancy produced a ton of HCG. I was over 5k at 4.5 weeks. By the end of 5 weeks, I was over 45k. Not twins either. To ease any anxiety, the abundance of HCG had nothing to do with the loss.
I would say wait until AT LEAST 10dpo. I'd say until AF is due but if you're like me then that is not happening.