Public Class frmPopUp

    Property CountdownStartSec As Int32
    Property TimeOpen As Int32 = 0
    Property Nachricht As String = ""
    Property CountdownIsStarted As Boolean = True

    Private Sub frmPopUp_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        MsgBox(Nachricht)
        lblNachricht.Text = Nachricht

        If CountdownIsStarted = True Then Timer1.Enabled = True
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        TimeOpen = TimeOpen + 1
        If CountdownStartSec > 0 Then
            lblCountdown.Text = (CountdownStartSec - TimeOpen).ToString
        Else
            Me.Close()
        End If
    End Sub
End Class