Ovulation test questions

How many days after a positive is it before you actually ovulate and how many before it’s too late? I’ve lost the instructions and can’t remember exactly. It said something like 24 hrs after as you’re about to ovulate in the next 2 days. But I don’t really know. Sorry for silly questions. I’ve had a positive yesterday and today’s is lighter. Have we missed it once it’s lighter the next day? Thank you in advance