Traffic
Engagement time
Also called active time.
Engagement time is the time a page was visible in the foreground and, in some models, receiving input. It replaces guesswork about the last page of a session.
How it is measured
A script watches visibility state and starts a timer when the tab is in front, then stops it when the tab is hidden or the user leaves. Some tools add keyboard, mouse or scroll signals to confirm someone is there. The unit is seconds per pageview or per session.
Tarsier sends an engagement ping every 15 seconds while the tab is visible, and one more when the page is hidden, so a background tab left open does not rack up time.
Worked example
A long-read essay is open in one tab for 41 minutes while the reader works in another. Under a loaded-time model that tab counts 41 minutes. Under engagement time it counts the 3 minutes 15 seconds when the tab was in front.
The writer sees a median of 2 minutes 50 seconds across the piece and realises that most people finish roughly the first third of a 3,000-word essay.
How it differs
Engagement time adds up visible seconds, while time on page is the gap between this pageview and the next hit. The first can be measured on the last page; the second cannot. Engaged time is a close variant that also requires activity signals.
Common errors
Assuming visible means reading. Counting time while the tab is behind another window. Comparing a tool that uses input signals to one that uses only visibility. Averaging across mobile and desktop without splitting them. Ignoring pages with video.
In practice
Use it for long-form pages and tools with a reading flow. Compare medians across articles of similar length. Do not set a global seconds target; set a target by page type.