What is Visit duration?
Visit duration is the elapsed time between the first and last recorded action of a visit. Because it is measured between timestamps, the time spent on the last page of a visit has no closing event to measure against and is usually counted as zero — which means single-page visits often record a duration of nothing at all.
The structural undercount
A visit with three pageviews at 10:00, 10:02 and 10:05 records five minutes — even if the visitor then spent ten minutes reading the third page. There is no fourth timestamp to subtract from, so the final stretch is invisible.
Consequences worth knowing:
- Single-page visits record zero, unless the tool sends periodic engagement signals.
- Averages are dragged down by every one of those zeros, which are usually the majority of visits.
- The undercount is worst where reading is deepest — a long article read to the end and closed contributes nothing.
How tools compensate
Some send periodic heartbeats while the page is visible, others send a final duration when the tab is hidden or closed. Both improve the number, and both cost extra requests from every visitor, which is a real trade against page weight and battery.
sonex measures engaged time and sends it with a later event rather than firing a beacon every few seconds, so the last page contributes without the visit costing a request per interval.
Reading it well
Never compare durations across tools — the measurement differs too much to mean anything. Within one tool, compare the same page over time, or two pages of the same kind against each other.
Pair it with bounce rate. Duration alone cannot separate a visitor who read carefully from one who left a tab open; bounce alone cannot separate a satisfied reader from an instant exit. Together they usually can.