as of version 1.4 you could use the following filter to disable pre-ordering between certain times.
for example if you close at 15:00 and need a couple of hours (i.e from 15:00 to 17:00) to make sure you have enough stock for the next day to be able to fulfill preorders for that day
will require php >=5.3

/*no (pre)order between 15:00 and 17:00 | DateTime php >=5.3 only */
add_filter( 'wppizza_po_filter_values', 'myprefix_wppizza_preorder_set_values' ,10 , 2 );
function myprefix_wppizza_preorder_set_values($values,$timestamp){
$close = DateTime::createFromFormat('H:i', '15:00')->getTimestamp();
$open = DateTime::createFromFormat('H:i', '17:00')->getTimestamp();
/**no order between these times*/
if ($timestamp > $close && $timestamp < $open){
$values['allowTimes']=array();
}
return $values;
}