It all depends upon how sensitive the HPT is and how quickly urine contains HCG. Some tests (First Response, Answer Early Result, internet cheapies, etc.) say that you can test up to 5 days before your missed period. Yet, if you look closely, the statistics for testing that early are really low. It's best to wait until you miss your period. However, if you can't wait, try one of those sensitive tests.
Some ladies you'll ask got their BFP 9dpo-18dpo and sometimes later. I got my first BFP around 12dpo-13dpo.
Good luck as you POAS; I hope your stay is short on the TTC board!!