twisted.protocols.ftp.FTP.ftp_MDTM(self, path) method documentation

File Modification Time (MDTM)

The FTP command, MODIFICATION TIME (MDTM), can be used to determine when a file in the server NVFS was last modified. This command has existed in many FTP servers for many years, as an adjunct to the REST command for STREAM mode, thus is widely available. However, where supported, the "modify" fact that can be provided in the result from the new MLST command is recommended as a superior alternative.

http://tools.ietf.org/html/rfc3659