I've always got an instant positive as soon as AF is due on the Clear Blue Digitals (so it says Pregnant). With DD1 I tested the day AF was due which was around 14 dpo and with DD2 it was the day before AF was due. I usually have a 28 day cycle. With DD1 I had a blood test that day (or the next, can't remember) and my HCG levels were only 63. I didn't bother finding out my HCG levels with DD2.

So for me they've been super accurate very early on, around 13-14 dpo. I hope your BFP is a real positive. Good luck