Hi @Aaron271 I hope you are well!
Think of your Airbnb calendar in nights not days, and things become easier to understand:
Guests stays run in number of nights (not days), so if you block Friday 10th May, a guest won't be able to book the night of Friday 10th May.
If Thursday 9th May is not blocked, then a guest can book it- and then check-out on morning of Friday 10th May.
If you want the entire day of Friday 10th May without the possibility of guests checking-out or in, you will need to block the 9th and 10th.
Best wishes
Paul.