从Datetime到Decimal的转换无效

Question

我试图将总时数列为总时数，如下所示：

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

    If DataGridView1.RowCount > 1 Then

        Dim IntTotalHours As Decimal = 0
        Dim IntPricePerhour As Integer = 0

        For Index As Integer = 0 To DataGridView1.RowCount - 1
            IntTotalHours += Convert.ToDecimal(DataGridView1.Rows(Index).Cells(2).Value)

        Next
        TextBox1.Text = IntTotalHours
        TextBox3.Text = FormatCurrency(IntTotalHours * 15)

    End If
End Sub

但我收到错误：

IntTotalHours += Convert.ToDecimal(DataGridView1.Rows(Index).Cells(2).Value)

如何使用datagridview将时间转换为十进制？