Public Class Form1
       Dim cambio As Boolean = false
       Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
           Dim url As String = ""
           If cambio Then
                url = "http://www.facebook.com"
           Else
                url = "https://www.google.es"
           End If
           cambio = Not cambio
           Process.Start(url)
       End Sub
 
       Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
           Timer1.Interval = 30000
       End Sub
    End Class