Confession incoming - I don't actually know how i'm meant to use these things, I've read a lot about ensuring you're DTD (doing the deed) in the lead up to ovulation and during, if this were in August should we have jumped straight into bed at 6.31pm yesterday?? How many 'prime' hours/days are there usually??
OPKs predict whether your body is about to try and ovulate, they don’t guarantee you absolutely have or will ovulate. But a positive OPK is a good sign that the hormone needed to release the egg is surging.
Ideally you want to be having sex in the days leading up to ovulation, even once in the three days prior to ovulation is sufficient to give you the best chance of conceiving, though I like many other women didn’t want to waste any opportunity and had sex every day around fertile week! But you don’t have to. Studies show that two days prior to ovulation is the date most likely to result in conception. You have to bear in mind that once your egg is released it’s only viable for 12-24 hours max, and sperm can take several hours to get to where it needs to be (5-7 hours on average). So if you’re solely waiting to have sex only once you get a positive OPK you may be too late.
OPKs are great as a sign your body is working as it should, even though they don’t prove ovulation, they’re especially useful when used every month during fertile week to get a feel for your cycle and on which day you tend to ovulate. But for the best chance of conception have sex every other day during the fertile window (the window of time leading up to ovulation) and no matter which specific day you ovulate you’ll have got the sperm where it needs to be.
I used an app called My Calendar which was helpful, plus we also used the OPKs and a sperm friendly lube (pre-seed), I had a positive OPK two days straight and we had sex three days before the first OPK, and on both positive OPK days, conceived the first month of trying. Wasn’t expecting it to happen so fast, I was just using the OPKs to see whether or not I was trying to ovulate given a history of endometriosis and knowing I only had one functioning tube (so with half my eggs going to waste I wanted to make every month count).
If you hadn’t been having sex leading up to the positive OPK I’d say it’s still worth leaping into bed ASAP to make the most of it but in future cycles you can time sex better so you’re doing more of it during fertile week.
I recommend a book called taking charge of your fertility, plus an awesome subreddit called trying for a baby, which has far more knowledgable posters than me and loads of really simple to understand scientifically backed information on improving your chances.