how to get window idle time

Question

I am new in vb.net WPF coding, need advice how to get idle time on window to prevent dispatcher timer if user is using app? dispatcher should execute only if window idle time is greater then 1 minute

Public Sub dispatcherTimer_Tick(ByVal sender As Object, ByVal e As EventArgs)
   naloziDGV1()
   naloziDGV2()
   naloziDGV3()
End Sub