code: def data_len_for_day(self, day):
          
          day_ix = self._session_labels.get_loc(day)
          # Add one to the 0-indexed day_ix to get the number of days.
          num_days = day_ix + 1
          return num_days * self._minutes_per_day
docs: Return the number of data points up to and including the
          provided day.