I think your best option is to do a date range search and put in the time... so if you delete line 44 from your results page and replace it with:
$WADbSearch1->addComparison("OrderDate","". (isset($_GET['OrderDate'])?date('Y-m-d 00:00:00',strtotime($_GET['OrderDate'])):""). "","AND",">=",2);
$WADbSearch1->addComparison("OrderDate","". (isset($_GET['OrderDate'])?date('Y-m-d 23:59:59',strtotime($_GET['OrderDate'])):""). "","AND","<=",2);
That should do the trick.