We segment every 24-hour day into 15-minute test intervals, numbered 0 to 95. This allows us to group test results into time periods that provide not just a reasonably high granularity but also an allowance for convenient and efficient impairment coalescing.

For example, if 50 packets were lost within a couple of minutes you wouldn't want 50 separate alerts. You would want a single alert indicating general packet loss, with details available if you're interested.