Another little handy tool; to get the most recent modified time from files in a directory. It even does recursive directories if you set the $doRecursive param to true. Based on a file/directory list function I saw somewhere on this site. ;)
function mostRecentModifiedFileTime($dirName,$doRecursive) {
 $d = dir($dirName);
 $lastModified = 0;
 while($entry = $d->read()) {
 if ($entry != "." && $entry != "..") {
 if (!is_dir($dirName."/".$entry)) {
 $currentModified = filemtime($dirName."/".$entry);
 } else if ($doRecursive && is_dir($dirName."/".$entry)) {
 $currentModified = mostRecentModifiedFileTime($dirName."/".$entry,true);
 }
 if ($currentModified > $lastModified){
 $lastModified = $currentModified;
 }
 }
 }
 $d->close();
 return $lastModified;
}