Date format and offset

$fromDate = "2017-06-01"; // change date here
$toDate = "2017-08-15"; // change date here
$fromDate = new Zend_Date(strtotime($fromDate . ' 00:00:01'));
$toDate = new Zend_Date(strtotime($toDate . ' 23:59:59'));

/* Get the collection */
$orders = Mage::getModel('sales/order')->getCollection()->addAttributeToFilter('created_at', array('from'=>date('Y-m-d H:i:s', strtotime($fromDate)), 'to'=>date('Y-m-d H:i:s', strtotime($toDate))));