I just bought a bunch of cheapy opk strips from Amazon but they didn't really come with any instructions. I know the basics but any tips or hints on how/when to use?

Is it true that you shouldn't use your first urine of the morning? I think it's going to be a little tricky to do it at work. I work at a small bank and there is only one bathroom (one toilet, no stalls). I work with all women but still. I guess I could hide out in the bathroom for the entire 5 minutes but on very busy days when you work with the public, 5 minutes is a long time to be away from my teller window! Can I do it as soon as I come home from work (varies between 4:15 & 6:15)?

ETA: My co-workers all know we're ttc but they're all of the "relax and it'll happen when you least expect" way of thinking. So to tell them I need 5 minutes everyday to pee on a stick may not go over so well.