Symfony2查找器组件。日期方法无法正常工作

我想删除超过一小时的文件

$finder = new Finder();
$finder->in($dir)->date('< 1 hour ago')->ignoreUnreadableDirs();
foreach ($finder as $file) {
    var_dump($file->getMTime() < strtotime('1 hour ago'));
}

这是错误的，文件在不到一个小时前确实发生了变化

$ date +'%F %T'
2013-10-16 11:23:03
$ ls -Gn --full-time
drwxrwxr-x 2 1000 4096 2013-08-05 15:45:31.295648000 +0400 dummy
drwxrwxr-x 2 1000 4096 2013-10-15 13:19:24.781790000 +0400 example
drwxrwxr-x 2 1000 4096 2013-10-16 11:02:10.152208721 +0400 test
-rw-rw-r-- 1 1000    0 2013-10-16 11:02:20.076209132 +0400 test_file1

我做错了什么

这是一只虫子

$ date +'%F %T'
2013-10-16 11:23:03
$ ls -Gn --full-time
drwxrwxr-x 2 1000 4096 2013-08-05 15:45:31.295648000 +0400 dummy
drwxrwxr-x 2 1000 4096 2013-10-15 13:19:24.781790000 +0400 example
drwxrwxr-x 2 1000 4096 2013-10-16 11:02:10.152208721 +0400 test
-rw-rw-r-- 1 1000    0 2013-10-16 11:02:20.076209132 +0400 test_file1