$re = '/^ # New line
T?([00-23]{2}) # Hour block (00 through 23 hours)
\:?([00-59]{2}) # Minute block (00 through 59 minutes)
\s* # Optional space
([ap])?\.?(m?)\.? # AM or PM, with or without periods
$ # End of the string./imx';
$str = 'T12:34
12:34
12:34PM
1000
12:34AM
12:34 AM
12:34 PM
12:34 A.M
12:34 P.M
23:59
23:59 PM
55:88 PM';
preg_match_all($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