In Next.js, time-based revalidation works like this: after the interval, the next visitor still gets the old page while a new one is built in the background, and the visitor after that gets the update. So the first person to look after the interval can see the old version.
On-demand revalidation removes most of that wait. When you publish, the site marks the stored copy invalid, and the next request rebuilds it. If the content lives in the code itself, a change needs a new deployment instead.
None of this needs live connections to visitors' browsers. That is a separate feature, for pages that must update while someone is looking at them, and it costs more to build and run. For most content, an interval of seconds plus a publish trigger is enough.
Updated October 2026
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