Add the class datecheck to your field "Destruction Date" then add the following into your javascript.

$(document).ready(function(){

  $('.datecheck').on('blur', 'input', validatedate);
    
    function validatedate() {
    text = $('.datecheck input'); 
    if (/\d+\/\d+\/\d{4}/.test(text))
    {// good input
    }
      else { // bad input
        $('.datecheck input').val('Please use mm/dd/yyyy format');
      }
    };

});

This will validate the input and change the value of the field to the message, "Please use dd/mm/yyyy format' whenever focus is shifted out of the date picker window.

Edit to your desire, you can use a pop-up dialog box, like what Laserfiche does to provide the red text notification of invalid input, instead of assigning the above text as well.

https://jqueryui.com/dialog/

Cheers