I Kept the Same 300 Test Durations and Changed Only Their Order. p95 and p99 Missed the Slow Streaks

After my previous experiments with test latency, I started wondering whether I was still looking at the wrong statistic.
Mean latency is obviously incomplete.
p95 is better.
p99 is useful when rare slow runs matter.
But all of these measurements have one property that is easy to overlook:
They do not care about order.
If I take 300 test durations and randomly rearrange them, the mean remains identical.
So do p50, p95 and p99.
The total waiting time is identical too.
Yet from a developer perspective, ten slow runs scattered across an afternoon do not necessarily feel like ten slow runs arriving almost back to back.
That gave me a very specific experiment.
I generated one set of 300 test durations.
Then I created two timelines from exactly the same values.
In the first timeline, durations were randomly ordered.
In the second, slow runs were deliberately clustered.
Nothing else changed.
The result surprised me more than changing the latency distribution itself.
Both timelines had:

















