<!DOCTYPE html>
<html>
<body>

<?php
$date=date_create("2016-09-25");

date_time_set($date,12,36);
echo date_format($date,"Y-m-d H:i:s") . "<br>";

date_time_set($date,11,25,56);
echo date_format($date,"Y-m-d H:i:s");
?>

</body>
</html>