IUI timing confusion

Melisa • 35, Finally pregnant with #1 after IVF!! Due in May 💗
I got a positive opk this morning (it was negative yesterday), so I scheduled my <a href="https://glowing.com/glow-fertility-program">IUI</a> for tomorrow. 
But when I input the data into glow it says today I have a 27% chance of pregnancy and tomorrow it's an 18% chance. I also use the Ovia app and the same thing, it has my fertility score yesterday as 10, today as 9.5, and tomorrow is 8.5. 
Does this mean tomorrow is too late? I had to wait for a positive to schedule it.