[Chronosphere docs]: use timestamp() and unless() with a 5-minute offset to spot gaps: query the metric and take the complement of the same metric offset by 5 minutes. Points only plot where the metric is missing now but was present 5 minutes ago, so filled portions mark outage windows and their length marks duration. To alert on missing metrics, look for values greater than zero in that pattern.

Context: Metrics go missing intermittently and you need a repeatable way to see when a Prometheus endpoint stopped emitting.