$re = '/\s(\d{2}\:\d{2}\s(?:AM|PM|am|pm))/';
$str = 'Time today is 10:30 pm
Time today is 10:30 PM
Time today is 10:30 AM
Time today is 10:30 am
Time today is noon';
preg_match_all($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