I would say you could probably get an accurate result after 12 dpo depending on the type of test. I think ff tells you to test wayyy late if you aren't sure of you LP.
With my last pregnancy I tested beginning at 9 dpo and didn't get a positive until 14 dpo. With my first pregnancy I wasn't charting or anything so I have no clue how many dpo I was when I got a positive.

I would say that I probably won't test again before 12 dpo (ugh...I say that now...LOL).