First time using OPK

Hi there , i'm first timer trying to use an opk. I've got a lot of questions i wanted to ask. Tried searching for answer on the net but still confused.1- When should i be using if my af starts on 22 may 12 (28 days cycle)2- can i test at 2pm and then test again later at 11pm? ( due to work)3-After getting a positive opk when is the best time to BD? If i tested positive at 2pm that day and by the time i reached home its already 11pm will it still be useful if BD that night?4-when should i stop opk after a positivePls Pls ans to my questions im in alot of doubts. Thanks all and lots of to all