public long getIdleExpirationTime() throws EntryNotFoundException {
    long idle = getIdleTimeoutInMillis();
    if (idle > 0) {
      return getLastAccessedTime() + idle;
    }
    return 0L;
  }
Return the absolute time when idle expiration occurs, or 0 if not used
geode-core/src/main/java/org/apache/geode/internal/cache/ExpiryTask.java