$re = '/^(?:(?:[0-1][0-9])|2[0-3]):[0-5][0-9]:[0-5][0-9]$/mi';
$str = '01:58:29
12:05:19
13:59:03
00:00:00
23:59:59
00:59:59
00:00:59
23:00:00
24:00:00
00:60:00
00:00:60';
preg_match_all($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