def start_time_from_tindex(tindex)
      if index_references_time(tindex)
        return @constructs[tindex].time
      elsif index_references_timespan(tindex)
        return @constructs[tindex].start_time
      else
        fail 'ConstructInterpreter#start_time_from_tindex says: tindex does not reference a time or time span'
      end
    end
def start_time_from_tindex(tindex)
      if index_references_time(tindex)
        return @constructs[tindex].time
      elsif index_references_timespan(tindex)
        return @constructs[tindex].start_time
      else
        fail 'ConstructInterpreter#start_time_from_tindex says: tindex does not reference a time or time span'
      end
    end
Returns either @time or @start_time, depending on whether tindex references a Time or TimeSpan construct