When do I ovulate?

A
I took my first ovulation test yesterday around lunch time. It didn't look like I was too far off from getting a positive (top picture). 
I took another test around the same time today, which was positive (bottom picture). 
I'm unsure of how long after getting a positive that you have before ovulation. Is there a certain time period? Could I have got my positive later in the day yesterday and missed ovulation? 
Sorry for all the questions. I've never tested for ovulation before and I'm trying to understand how it all work. 

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