Timer1.Interval = 5 * 1000

Public Class Form1
 
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ListBox1.Items.Add(TextBox1.Text) ' Añadimos el dato
        TextBox1.SelectAll() ' Seleccionamos el texto
        TextBox1.Select() ' y activamos el TextBox
    End Sub
 
    Private Sub Timer1_Tick(Sender As Object, e As EventArgs) Handles Timer1.Tick
        Static i As Integer = 0
 
        If i = ListBox1.Items.Count Then
            Sender.Stop()
            i = 0
            MsgBox("Terminó la lista")
        Else
            ListBox1.SelectedIndex = i
            WebBrowser1.Navigate(ListBox1.SelectedItem)
            Me.Text = "Navegando en '" & ListBox1.SelectedItem & "'"
            i += 1
        End If
 
    End Sub
 
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Timer1.Interval = 5 * 1000
        Timer1.Start()
    End Sub
 
End Class

Public Class Form1
 
    Dim Seconds As Long = 0
 
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ListBox1.Items.Add(TextBox1.Text) ' Añadimos el dato
        TextBox1.SelectAll() ' Seleccionamos el texto
        TextBox1.Select() ' y activamos el TextBox
    End Sub
 
    Private Sub NavigateListBox()
        For Each URL As String In ListBox1.Items
            Me.Text = "Navegando en '" & URL & "'"
            WebBrowser1.Navigate(URL)
            Sleep(Seconds) ' Segundos
        Next
    End Sub
 
    Private Sub Sleep(ByVal Duration As Int64)
        Dim Starttime = DateTime.Now
        Do While (DateTime.Now - Starttime).TotalSeconds < Duration : Application.DoEvents() : Loop
    End Sub
 
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        NavigateListBox()
    End Sub
 
    Private Sub TextBox2_TextChanged(sender As Object, e As EventArgs) Handles TextBox2.TextChanged
        Seconds = CLng(sender.text)
    End Sub
 
End Class