Sort Orders by delivery date.

Hi there. I want to ask you if there some way to set the orders in the backend by delivery date. Obviously I have Order Delivery Date plugin installed.
Actually I saw there's a piece of the code used in the customer page to order in desc and asc way the data in the order.php page.

switch ($_GET['list_order']) {
	      case "delivery-date":
              $disp_order = "o.order_delivery_date";
              break;
              case "delivery-date-desc":
              $disp_order = "o.order_delivery_date DESC";
              break;
              default:                       
			  }
?>
 <td class="dataTableHeadingContent" align="center"><?php echo TABLE_HEADING_DELIVERY_DATE; ?>
>a href="<?php echo zen_href_link(basename($PHP_SELF) . '?list_order=delivery-date', '', 'NONSSL'); ?>"><?php echo ($_GET['list_order']=='delivery-date' ? '<span class="SortOrderHeader">Asc</span>' : '<span class="SortOrderHeaderLink">Asc</b>'); ?></a>
<a href="<?php echo zen_href_link(basename($PHP_SELF) . '?list_order=delivery-date-desc', '', 'NONSSL'); ?>"><?php echo ($_GET['list_order']=='delivery-date-desc' ? '<span class="SortOrderHeader">Desc</span>' : '<span class="SortOrderHeaderLink">Desc</b>'); ?></a> </td>

I dont understand so much how this "list_order" works so any help very appreciated.