You will see min and max stay, under that is "Add another requirement". By choosing that you can specify during which period you want X days for minimum stay.
If I select a minimum stay of 3 nights then add in "extra requirements" 3 nights stay only in the month of July, the guests will not be able to do an instant 3 night booking for say August in which I only allow minimum 5 nights?
@John850 i suggest you to set minimum lenght as you plan and then check availability on your own as you were a guest to see if it is like you wanted to be 🙂