- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
$dateTime = '2007-01-11 12:34:56';
preg_match('~(\d{4}-\d{2}-\d{2})\s?(\d{2}:\d{2}:\d{2})?~', $dateTime, $matches);
$matches['time'] = array_key_exists('time', $matches) ? $matches['time'] : '00:00:00';
var_dump($matches);