Hello,
ftp.GetFileDateTime(remotepath) method automatically uses MLST command since version 2012R2 (if supported by the server). To take advantage of this, an update to at least version 2012R2 is required.
For more details on how to get the new version see my comment to your comment at the original question.
With 2012R1 and earlier, you can use the following method to determine file date/time using MLST command:
Public Ahared Function GetFileDateTime(ftp As Ftp, path As String) as DateTime
ftp.SendCommand("MLST " & path)
Dim res As ftpresponse = ftp.ReadResponse()
If res.Group <> 2 Then Throw New FtpException(res)
dim facts As String = res.Raw.Split(Chr(10))(1).Trim()
Dim raw() As String = { facts }
Dim items = New FtpItemCollection(raw, FtpListingType.MachineProcessingList)
Return items(0).LastWriteTime.Value
End Function