How do OPK tests work really?

Beth • Newlywed with 7 and 2 year old girls .. trying for #3
Okay I got a positive yesterday morning and an even bolder positive last night. Took one this morning and it is still pretty dark. So I'm guessing my LH surge was yesterday evening. If we have sex tonight should that be good? We have BDed on Late late Sunday/ early Monday morning, late late Tuesday night. So we skipped yesterday but pretty sure if we BD tonight and tomorrow it'll be a good chance. I didn't want to BD yesterday even though I got the positive because I've read BD every other day is better to allow sperm build up. Sound like a plan?