code: private long getNow()
      {
          return Collections.max(cfs.getSSTables(), new Comparator<SSTableReader>()
          {
              public int compare(SSTableReader o1, SSTableReader o2)
              {
                  return Long.compare(o1.getMaxTimestamp(), o2.getMaxTimestamp());
              }
          }).getMaxTimestamp();
      }
docs: Gets the timestamp that DateTieredCompactionStrategy considers to be the "current time".
  @return the maximum timestamp across all SSTables.
  @throws java.util.NoSuchElementException if there are no SSTables.