Visual Basic.NET - calcular diferencia de fechas y horas

Private Sub Calcular_Tiempo_Faltante()

        Dim ta As String = Format(System.DateTime.Now, "HH:mm")

        Dim Resto As Integer = 0

        Dim F1 As DateTime = Tbl_Visitas.RowActual("Fec_Visita")                    ' fecha de inicio

        Dim F2 As DateTime = Tbl_Visitas.RowActual("Fecha_Salida")                    ' fecha de salida

        Dim Fa As DateTime = Format(System.DateTime.Now, "dd/MM/yyyy")     ' Fecha actual 

        Dim H1 As DateTime = Tbl_Visitas.RowActual("Hora_Ingreso")                  ' Hora de inicio

        Dim H2 As DateTime = Tbl_Visitas.RowActual("Hora_Salida")                   ' Hora de Salida

        H2 = Format(System.DateTime.Now, "HH:mm")

        Dim D As Integer = Tbl_Visitas.RowActual("Horas_Visita")             ' duracion en horas

        Dim T1 As DateTime = Format(F1, "dd/MM/yyyy") & " " & Format(H1, "HH:mm:ss")

        Dim T2 As DateTime = Format(Fa, "dd/MM/yyyy") & " " & Format(H2, "HH:mm:ss")

        Dim Tf As Long

        T1 = DateAdd(DateInterval.Hour, D, T1)

        'Lbl_Hora.Text = DateDiff(DateInterval.Hour, t2, t1, FirstDayOfWeek.Monday)

        'Lbl_Min.Text = DateDiff(DateInterval.Minute, t2, t1, FirstDayOfWeek.Monday)

        'Lbl_Sec.Text = DateDiff(DateInterval.Second, t2, t1, FirstDayOfWeek.Monday) / 3600

        Tf = DateDiff(DateInterval.Second, t2, t1)

        'Debug.Print("Horas: ", Lbl_Hora.Text) 'String.Format("{0:d/M/yyyy HH:mm:ss}", Tf))

        'Debug.Print("Min: ", Lbl_Min.Text)

        'Debug.Print("Seg: ", Lbl_Sec.Text)

        ' Lbl_T_Restante.Text = String.Format("0:{HH:mm:ss}", Tf) + " / " + Lbl_Hora.Text & " : " & Lbl_Min.Text & " : " & Lbl_Sec.Text

        Lbl_T_Restante.Text = sTiempo(t1, t2)

        '   Me.Refresh()

    End Sub

    Private Sub PictureBox1_Click(sender As System.Object, e As System.EventArgs) Handles PictureBox1.Click

        Try

            Calcular_tiempo_Faltante()

        Catch ex As Exception

        End Try

    End Sub

    Function sTiempo(dInicio As Date, dFin As Date) As String

        Dim Tiempo As String

        Tiempo = Str((DateDiff("s", dInicio, dFin) \ 86400) Mod 365) & " días, "

        Tiempo = Tiempo & Str((DateDiff("s", dInicio, dFin) \ 3600) Mod 24) & " horas, "

        Lbl_Hora.Text = Str((DateDiff("s", dInicio, dFin) \ 3600) Mod 24)

        Tiempo = Tiempo & Str((DateDiff("s", dInicio, dFin) \ 60) Mod 60) & " minutos, "

        Lbl_Min.Text = Str((DateDiff("s", dInicio, dFin) \ 60) Mod 60)

        Tiempo = Tiempo & Str(DateDiff("s", dInicio, dFin) Mod 60) & " segundos."

        Lbl_Sec.Text = 0

        sTiempo = Tiempo

    End Function

Dim ts As TimeSpan = Convert.ToDateTime(thora_sal_x).Subtract(Convert.ToDateTime(thora_ent_x))

Dim horas As Int32 = ts.Hours

Dim minutos As Int32 = ts.Minutes