DispatcherTimer.Interval Property

private void TestDispatcherTimer(Panel counterPanel)
{
    DispatcherTimer timer = new DispatcherTimer();
    int counter = 0;

    counterPanel.MouseLeftButtonDown += 
        delegate(object s, MouseButtonEventArgs args) {
            if (timer.IsEnabled) timer.Stop(); else timer.Start(); 
        };

    timer.Tick += 
        delegate(object s, EventArgs args) {
            counterPanel.Children.Clear();
            counterPanel.Children.Add( new TextBlock { 
                Text = counter++.ToString() });
        };

    timer.Interval = new TimeSpan(0, 0, 1); // one second
    timer.Start();
}