you mean in the search form right?
yes, you could do that, but on the results page, you need to add code to reformat the date. your search form has the date field named "DateSearch"
so add the following code at line 1 to reformat the date to use the yyyy-mm-dd format:
<?php
if(isset($_POST['DateSearch'])) {
$_POST['DateSearch'] = date("Y-m-d", strtotime($_POST['DateSearch']));
}
?>