$re = '/\d+:\d+(?::\d+)?(*SKIP)(*F)|:\w+/m';
$str = '2018-05-21T00:00:00+02:00
00:00:00
00:00
:light at 07:15:0000';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php