WHAT TIME TO TAKE AN OPK TEST?

Mom of Boys • Mom of boys ages 9 and 4. Third baby boy born Jan 2nd 2018 💕
I'm confused as to when I should be taking OPKs. I was doing first morning urine and then at night like 3 hrs before bed. I read to not use first Morning urine and to test from 11 to 3 pm and then take a second from 5 to 10pm. Is that true?? Help please!! I don't want to miss my O.