I’m wanting to update a textblock in wpf form with a countdown timer on the press of a button.
At the moment it looks like the tick event of my DispatcherTimer is not being invoked.

This is the entirety of my code in vb.net

Private WithEvents tm5min As New DispatcherTimer
Private Sub BtnStart5_MouseDown(sender As Object, e As MouseButtonEventArgs) Handles BtnStart5.MouseDown
        Try
            tm5min.Interval = TimeSpan.FromMinutes(5)
            tm5min.Start()
            Debug.WriteLine("clock started with: " & tm5min.Interval.TotalMinutes)
        Catch ex As Exception
            Debug.Write(ex.Message)
        End Try
End Sub

Private Sub tm5min_Tick(sender As Object, e As EventArgs) Handles tm5min.Tick
        Debug.Write("I'm ticking")
        TxtCountdown.Text = Date.Now.ToString("mm:ss")
End Sub