OPK questions!

I just started using opk’s for the very first time. My cycle is irregular because it’s adjusting after breastfeeding for 13 months. I took my first opk this morning and it was pretty dark, almost as dark as the control line, so I took another later this evening and it was lighter. My main question is, since I obviously had already peaked, how long does it take the LH to decrease? I’m really just trying to pinpoint when I actually ovulated. I know it’ll be hard to tell the exact moment it happened, but for those of you who have been doing this a while, what is your opinion? Do you think I ovulated yesterday, or maybe today even though the LH is decreasing?

Thank you I’m advance!