I don't think anyone can answer that for certain since everyone's cycles are different but personally, I'd give it 14 days after possible ovulation so CD32. If you haven't AF by then, you should be able to test fairly accurately. If it tests negative, keep in mind that hcg slowly builds in your system so give it another 3-5 days (CD 35-37) and test again. Are your cycles fairly regular? How long are they usually? Do you know how long your luteal phase is?