I'm having such a hard time with OPKs this cycle. I don't feel like they are getting darker. I did take one at 3:30 this afternoon (2nd to last) and it was the darkest one I've had. When I got home tonight I took the last one at 11pm and it was lighter than the one earlier. The last one on the 28th looked to be getting darker to me, so now I feel like I must have ovulated sometime in the past 24-36 hours. The pictures don't do the shade difference justice. Or maybe I'm just seeing things!