When to take opk? 8-5 schedule

I work 8-5 everyday. When would be ideal for me to take ovulation tests? I've been testing since cd10 and I'm on cd18 now. Had a few that were close to being pos, but I'm wondering if my timing threw the tests off. I've been testing after I wake up sometime around 6am and in the evening when I get home between 530-6pm. If I can, I'll test on my lunch break, usually 1230pm. I drink alot of water and holding my urine is hard for me(small bladder). I've read where you need to hold your pee for 4 hours before testing!