long getExpiryMillis() throws EntryNotFoundException {
    long extm = getExpirationTime() - getNow();
    if (extm < 0L) {
      return 0L;
    } else {
      return extm;
    }
  }
Returns the number of milliseconds until this task should expire. The return value will never
be negative.
geode-core/src/main/java/org/apache/geode/internal/cache/ExpiryTask.java