TimeStamp comparison

Question

Hi

   I have below code. I want tots should be greater than frts else error message should get displayed.

 String frTime = ddlTimeFrom.SelectedItem.Value;
                        var frts = TimeSpan.Parse(frTime);
                        String toTime = ddlTimeTo.SelectedItem.Value;
                        var tots = TimeSpan.Parse(toTime);

Thanks