OPK experience -- 7 hour window for positive

We are trying naturally til the next (and last) ivf with my own eggs. So, I bought a bunch of opks, which I have not used for years. I had the Clear Blue Easy Monitor last year, but that did not work, I would get days and days of high fertility.

Anyway, based on what I read, seeing lots of ewcm, and knowing I almost always o on Day 11 or 12, I started peeing on them every 4-6 hours today, CD11. I have been getting close to a positive (two solid lines).

Just today:

8am two lines, close but not both dark enough
12 noon Positive -- the second line is finally darker than the test line
7pm -- Back to the same lines as this morning: one dark, one nearly as dark.

I am assuming that I am o'ing tonight or tomorrow, since all the signs are there (pain in the side, etc.)

How many of us do you think have such a short window? How would most people catch it? Does this I might be able to target my o better, since I know a finite window of the surge?