OPK- What time of day to test?

I got some Accumed opk tests and the instructions said it doesn't matter when to take the test, just do it at the same time each day. I have read mixed reviews on FMU versus late afternoon/early evening testing. Today was my first day using them and I did one this morning around 7:30am and one around 7:30pm. The one this morning was negative, but darker than the one I did when I got home from work. Should I trust the darker FMU one, or the lighter evening one? I cannot test at work, so between 10am and 6pm won't work for me. So I either have to do it in the morning or in the evening. I didn't drink anything or pee for over 2 hours before taking the test in the evening either. HELP!