Only way to change modification date in catalogue is to create file in via touch() and dalete it with unlink():
<?php
$dir = 'temp';
$files1 = scandir($dir);
$files1 = array_slice($files1, 2);
foreach ($files1 as $key => $val) 
{
 if (!is_dir($val)) continue;
 if (!touch($val)) 
 {
 touch($val . "/plik.txt");
 unlink($val . "/plik.txt");
 }
}
?>