When not enough data (just one instance recorded) show NA instead of 0ns

See in this screenshot we have an API that was hit exactly one time.

<img width="517" src="https://api.zenhub.com/attachedFiles/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBBOG1YQmc9PSIsImV4cCI6bnVsbCwicHVyIjoiYmxvYl9pZCJ9fQ==--083c4abe642be83fd4574fbf0405c6ef233279df/image.png" alt="image.png" />

