Hello,
please use the GetFileDateTime() method of the Ftp class to get the modification date and time of the specified remote file, e.g.
// connect and login...
Ftp ftp = new Ftp();
ftp.Connect(...);
ftp.Login(...);
// get the modification datetime
DateTime dt = ftp.GetFileDateTime("fileName");
The GetFileDateTime method represents the FTP MDTM command. Please note the MDTM command was not defined by the original RFC, but it has been widely supported for a number of years. And also please note some servers return times in their local time zones, some use GMT.