Public Shared Function GetFolderCreationTimeLimits3 _
                      (ByVal folder As String, _
                       ByVal criticalday As Date, _
                       ByRef mintime As Date, _
                       ByRef maxtime As Date) As Boolean
 
    mintime = New Date(2100, 12, 31)
    maxtime = New Date(1900, 1, 1)
 
    If Not IO.Directory.Exists(folder) Then Return False
 
    Try
       For Each file As String In IO.Directory.GetFiles(folder)
          Dim fi As New IO.FileInfo(file)
          fi.Refresh() 'in VB-Doku empfohlen !!
          Dim ct As Date = fi.CreationTime
          If ct.Date = criticalday.Date Then
             If mintime > ct Then mintime = ct
             If maxtime < ct Then maxtime = ct
          End If
       Next file
       Return True
    Catch
       Return False
    End Try
 
End Function

Dim mintime, maxtime As Date
 
lblCriticalday.Text = "27.3.2015" 'Zeichenfolge in Label-Eigenschaft
 
Dim folder As String = "C:\daten" 'zu durchsuchender Ordner
 
Dim criticalday As Date = CDate(lblCriticalday.text) 'Umwandlung in Date
 
If Not GetFolderCreationTimeLimits3 _
            (folder, criticalday, mintime, maxtime) Then
   MsgBox("Fehler")
Else
   lblMintime.Text = mintime.ToString("g") 'Formatierung von Date als String
   lblmaxtime.Text = maxtime.ToString("g")
End If