Ovulation tests

Heidi

I'm confused about these ovulation tests! Ok so it says dont use FMU. But also says make sure its concentrated enough. I have the BB femometer app and it says test between 12 & 8 pm and read at 5 minutes. Does it become invalid after 5 minutes? Glow says I ovulate tomorrow but Monday I had heavy EW CM but ovulation test was negative. Today my test was dark