public static long calcPositiveIntervalByMonth(
      long startTime, TimeDuration duration, ZoneId zoneId) {
    return TimeDuration.calcPositiveIntervalByMonth(
        startTime, duration, TimeZone.getTimeZone(zoneId), TimestampPrecisionUtils.currPrecision);
  }
convert duration string to millisecond, microsecond or nanosecond.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/utils/DateTimeUtils.java