code: @Override
    public int compareTo(TtlBucket ttlBucket) {
      long startTime1 = getTtlIntervalStartTimeMs();
      long startTime2 = ttlBucket.getTtlIntervalStartTimeMs();
      return Long.compare(startTime1, startTime2);
    }
docs: Compares this bucket's TTL interval start time to that of another bucket.
  
  @param ttlBucket the bucket to be compared to
  @return 0 when return values of {@link #getTtlIntervalStartTimeMs()} from the two buckets are
  the same, -1 when that value of current instance is smaller, otherwise, 1