Private Function LastFileDate(ByVal folder As String) As Date
 
    Dim maxdate As Date = Nothing
 
    For Each file As String In IO.Directory.GetFiles _
            (folder, "*.*", IO.SearchOption.TopDirectoryOnly)
       Dim fi As New IO.FileInfo(file)
       Dim ct As Date = fi.CreationTime
 
       'Ausschluss der heutigen Files
       If ct.Date < Today.Date Then
          'Suche nach dem größten Datum (ohne heute)
          If ct.Date > maxdate Then maxdate = ct.Date
       End If
    Next file
    Return maxdate
 End Function

  Dim lfd As Date = LastFileDate("C:\daten")
  If lfd <> Nothing Then
     MsgBox("Letzte Datei-Erstellung: " & lfd.ToString("dd.MM.yyyy"))
  Else
     MsgBox("Kein Datum gefunden")
  End If