I wouldn't go by it after they say not to. Try again with first morning urine.
I did, I took one, I read it really quick, like gave it less than a minute, negative, so I threw it away, came back a few hours later and it was positive. I think it was positive before the ten minutes though, and I just didn't look. Definitely keep testing!
could be an evaporation line that you were seeing which is why they give you the time limit to look at it with in. If you think you might be pregnant and it is early could always ask your doctor for a blood test.