Ovulation help

My husband and I conceived our first without any trouble, however this time around it's proven to be more difficult for us. So we started using ovulation predictor kits. I experienced EWCM Saturday night at work around 2200-2300. I took an OPK that night for curiosity and it was negative but still much darker than I was used to seeing. Sunday night my husband and I had sex. Monday morning I got my first dark positive OPK. We BD'd that night as well and just because I was excited and had never had a positive OPK I took another and it was still very positive that night even with slightly diluted urine. This morning, I took another and it was still a darker line than I was used to seeing before the positive but technically negative.

My husband and I work opposite shifts so we could only BD the day before my positive and the day of. I hope I'm not out this month because of that :(

I guess my question is once you're LH starts to go down does that mean you are no longer fertile and that the egg is no longer alive?

Are ovulation tests only positive 12-36 hours BEFORE ovulation or during ovulation as well?

Sorry for all the questions. I'm new to OPKS.