pretty ragin positive opk

Ashley • Pregnant with child #4 after 16 months of unexplained infertility. Just trying to look towards the future. 💋💍🥀🌮🍕🍻🍾 I love my 3 children, MTV's The Challenge & Greys Anatomy!s
Here is my question!
How does it go from negative to raging positive to quick?
I thought they are supposed to get gradually darker??
1st one taken last night @ 11:00pm
2nd one taken @ 7:45pm tonight