public long getEventTime(long suggestedTime) {
    long result = suggestedTime;
    if (versionTag != null && getRegion().getConcurrencyChecksEnabled()) {
      if (suggestedTime != 0) {
        versionTag.setVersionTimeStamp(suggestedTime);
      } else {
        result = versionTag.getVersionTimeStamp();
      }
    }
    if (result <= 0) {
      InternalRegion region = getRegion();
      if (region != null) {
        result = region.cacheTimeMillis();
      } else {
        result = System.currentTimeMillis();
      }
    }
    return result;
  }
this method joins together version tag timestamps and the "lastModified" timestamps generated
and stored in entries. If a change does not already carry a lastModified timestamp

@return the timestamp to store in the entry
geode-core/src/main/java/org/apache/geode/internal/cache/EntryEventImpl.java