“Online” sounds simple, but it is a derived state. Most endpoint platforms infer it from the most recent successful communication between an agent and a control plane.
Heartbeat interval
If an agent checks in every 30 seconds, a platform should not normally mark it offline after 31 seconds. Networks jitter, laptops sleep and processes can briefly pause.
Status threshold
A useful threshold creates tolerance. For example, a 30-second heartbeat might use a 90-second online threshold. That gives the device several opportunities to report before the UI changes state.
Stale versus offline
At larger scale it can be useful to distinguish online, stale and offline. A stale state tells an operator that evidence is getting old without immediately declaring failure.
Store timestamps consistently
Store server timestamps in a consistent standard such as UTC and convert them for the viewer in the browser. That prevents multi-country fleets from mixing storage logic with presentation logic.
Why this matters
Operational decisions should not be driven by an attractive green dot unless the platform can explain exactly how that dot was calculated.