$re = '/^([0-1]?[0-9]|2[0-3]):[0|3][0]\s[A|P]M$/m';
$str = '9:00 AM
12:30 PM
3:30 PM
5:00 PM
12:30 PM
12:34 AM
3:21 PM
4:56 AM';
preg_match_all($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