code: func nodeConditionsObservedSince(observedAt nodeConditionsObservedAt, period time.Duration, now time.Time) []v1.NodeConditionType {
  	results := []v1.NodeConditionType{}
  	for nodeCondition, at := range observedAt {
  		duration := now.Sub(at)
  		if duration < period {
  			results = append(results, nodeCondition)
  		}
  	}
  	return results
  }
docs: // nodeConditionsObservedSince returns the set of conditions that have been observed within the specified period