Once you have timed a thing a thousand times, you have to summarise it, and the obvious way is the wrong one.
Percentiles
Also called p50, p95, p99
Sort every timing from fastest to slowest. The 95th percentile, or p95, is the value that 95% of them are at or under. p50 is the middle one. A percentile is a time someone really waited, which an average need not be.
An agent asked if a change helped will often quote an average, because an average is what a quick script prints. A few very slow requests drag it up to a value nobody experienced, and a real regression for 5% of people can barely move it. Ask for the percentiles.
“Don't give me the average. Report p50, p95 and p99 for this endpoint, the sample size and the time window, before and after your change.”