Calculate days using timespan between 2 Datetimepicker

Question

I use this code and nothing works out :((

Dim FirstDate As Date

        Dim SecondDate As Date

        Dim ts As TimeSpan

        Dim diff As Integer

        FirstDate = DateTimePicker1.Value

        SecondDate = DateTimePicker2.Value

        ts = SecondDate - FirstDate

        If txtTOTAL_DAYS.Text = "" Then

            diff = ts.Days

            txtTOTAL_DAYS.Text = diff.ToString()

        End If

    End Sub

how to calculate timespan between 2 Datetimepicker? after the user select those datetimepicker, then the txtTOTAL_DAYS show automatically the total days between 2 datetimepicker.

Saturday and Sunday doesn't need to count.