Drag a timer control from your toolbox and double click on it and type this code :
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
Label1.Visible = Not Label1.Visible
Label2.Visible = Not Label2.Visible
End Sub
Make sure that your timer Enabled property is true.
I hope this will work.. :-)