code: func (s Storage) GetConsistencyTime(c context.Context) (time.Time, error) {
  	c = defaultContext(c)
  	latest := latestSettings()
  	switch err := ds.Get(c, &latest); err {
  	case nil:
  		return latest.When.Add(s.expirationDuration(c)), nil
  	case ds.ErrNoSuchEntity:
  		return time.Time{}, nil
  	default:
  		return time.Time{}, transient.Tag.Apply(err)
  	}
  }
docs: // GetConsistencyTime returns "last modification time" + "expiration period".
  //
  // It indicates moment in time when last setting change is fully propagated to
  // all instances.
  //
  // Returns zero time if there are no settings stored.