@Override
  public long cacheTimeMillis() {
    return system.getClock().cacheTimeMillis();
  }
Returns the current "cache time" in milliseconds since the epoch. The "cache time" takes into
account skew among the local clocks on the various machines involved in the cache.
geode-core/src/main/java/org/apache/geode/distributed/internal/ClusterDistributionManager.java