After many years of failed ttc and unsuccessful use of opks, I know I got pregnant this time in a cycle when I gave up on opks. I had a day of major ewcm and even though it was only about CD8, I thought what the hell and we DTD.
DH and I were ill for the rest of the cycle and didn't BD again. I got my BFP on CD28 when AF was due. Even though I should have thought it was waaaaaay too early to OV, my body gave me an unmistakable sign to get on with it. Listen to your body first, I'd say.
Good luck.