Fill in a specified number of times a form

Hello, (chronoforms V5)
I have an on-line booking form at school.

for the stage field there are 6 dates available in a dropdown.

I wish that no more than 20 recordings can be made for a given date.

Or at the 21st, should not the affected date be visible?

Or any form of impediment for no more than 20 recordings for that date.

thank you