Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Dim dt As DateTime
        If DateTime.TryParse(TextBox1.Text, dt) Then
            TextBox1.Text = dt.AddHours(12)
        Else
            MsgBox("Datum ungültig!")
        End If
    End Sub

Those people who think they know everything are a great annoyance to those of us who do - Isaac Asimov