Hi Walking Art
You should not do an OPK with FMU - you are trying to detect a surge and as your wee will be concentrated in the morning it is likely to show a surge even if there is not one there. Sorry to be the bearer of potentially bad news - you can easily only get the +ve for one day and this will be 12-24 hrs before you ovulate.

You should test around 10am, 3pm and 8pm I think as these are times when you are likely to detect the surge - saying that I never got a positive on an OPK and I used 100s of them.

Good luck.