$re = '/^(([[0|1]\d)|(2[0-3]))[:]?([0-5]\d)$/mi';
$str = '12
1300
1459
1760
2567
3382
2400
23:59';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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