Hello,
UPDATE: addProperties allows setting created and modified dates:
$properties = array(
'created' => '2016-11-21T09:00:00Z', // force a value
'modified' => substr(date(DATE_W3C), 0, 19) . 'Z', // dynamic value
'lastModifiedBy' => 'phpdocxuser',
);
$docx->addProperties($properties);
Regards.