LH increases and decreases

So when you have an LH surge (positive opk) that means you will ovulate within 24-36 hrs.. but then you keep peeing on the opk and if the test strip is light/faint the next day does that mean your ovulation is complete? Like it happened within that 24 hrs? Or if it stays dark for example does that mean you are ovulating currently and then when it goes light again you've stopped? I'm new to the opks and trying to understand. I understand the dark test strip is positive and ovulation will occur, but how do I know it has happened and finished if you get what I mean?