HPT: DPO or Days before AF?

Which is more important when deciding how early you can take a pregnancy test, DPO (days past ovulation) or days before missed period? Took one today (knowing I was kind of early) and got a BFN of course. I'm 8DPO, but since I ovulated late I'm on cycle day 26, just a couple days before missed period (or 4 days if I have a 30day cycle like Glow is predicting). I'm using the cheap little strip tests, but the website claims you can test up to 5 days before missed period. Thoughts?