Enable a custom date range datepicker in Woocommerce checkout

Solution:

This information is available in the jQueryUI documentation. Here’s an example of restricting the user to only allow a date 20 days in the past and 1 month + 20 days into the future. Replace your current $("#datepicker").datepicker(); declaration with the following

<script>
  jQuery( function() {
    $( "#datepicker" ).datepicker({ minDate: -20, maxDate: "+1M +10D" });
  } );
  </script>