php: delete file if exists more than 3 hrs

del_file.php

<?php
//Delete file if it exists for more than 3 hrs
$path = $_SERVER['DOCUMENT_ROOT']."/delete_test_files";

if ($handle = opendir($path)) {
    while (false !== ($entry = readdir($handle))) {
        if ($entry != "." && $entry != ".." && preg_match('/.*.ps/i', $entry)) {
            $last_modified = filemtime($path .'/' . $entry);
            $last_modified_str = date("Y-m-d H:i:s", $last_modified);

            $from_time = strtotime($last_modified_str);
            $to_time = strtotime(date('Y-m-d H:i:s'));
            $time_diff = ((round(abs($to_time - $from_time)) / 60))/60;

            echo $time_diff;

            if ($time_diff >= 3) {
                unlink($path . '/' . $entry);
            }
        }
    }
    closedir($handle);
}