If you create a file and then delete it, then you have modified the directory. In that case, the modtime of the directory wil be updated when u deleted the file.
Directory Modified Time is earlier than the files it contains for some
of my folders on HDFS. Is this usual? I would like to be able to
hadoop fs -rmr /path/to/some/dir
if the dirs modified time is older than 5 days or whatever.