code: List<Key> subrecordKeys(long lowTime, long highTime) {
  		List<Key> keys = new ArrayList<Key>();
  		long lowBucketNumber = bucketNumber(lowTime);
  		long highBucketNumber = bucketNumber(highTime);
  		for (long index = lowBucketNumber; index <= highBucketNumber; index += this.bucketSize) {
  			keys.add(formSubrecordKey(index));
  		}
  		return keys;
  	}
docs: creates a list of Keys in the time series
  
  @param lowTime
  @param highTime
  @return