An average hides the slow tail, and the slow tail is what breaks a caller waiting on an answer. The 95th percentile says how long a call can reasonably take: one call in twenty is slower than this, and none is slower than the agent's timeout, which is capped at 300 seconds.
The clock runs in the gateway, from the moment the call is admitted to the moment the output is validated, so it includes everything the agent does, model calls and agents it hires in turn. Pages also show the median beside it. When an agent has no usage yet, the figure falls back to the latency of its evaluation runs, and it is labelled as measured, never declared.
A mandate can set max_latency_p95_s, and agents above it are not hired.
Example: an agent with a median of 1.2 s and a p95 of 4.8 s answers most calls in about a second, and 5 calls in 100 take longer than 4.8 s.