code: public UserStatListResult getUserStatistic(String startTime, int duration)
              throws APIConnectionException, APIRequestException {
          return _reportClient.getUserStatistic(startTime, duration);
      }
docs: Get user statistic, now time unit only supports DAY
  @param startTime start time, format: yyyy-MM-dd
  @param duration 0-60
  @return {@link UserStatListResult}
  @throws APIConnectionException connect exception
  @throws APIRequestException request exception