For the benifit of other forum members, this is what I found to work. You can use the $newExpiryDate_MySQL in your MySQL record update/insert.
<?php
//CONVERT NEW PASS EXPIRY DATE $newExpiryDate_MySQL
$newExpiryDate_MySQL = date("Y-m-d H:i:s", $newExpiryDate);
//echo $newExpiryDate_MySQL
?>