A control-room terminal sits unattended between vessel movements. An open session on an unlocked screen means anybody walking past can record a move as somebody else, so sessions end after a period of inactivity.
An account owner sets the idle timeout under Settings → Session security, between 5 minutes and 12 hours. How long is tolerable is a judgement about your premises — a manned VTS desk and a shared tablet on a quay do not want the same number — so it is yours to make rather than ours.
Where no value has been chosen, the default is 30 minutes, and the settings page says so rather than presenting the default as a decision somebody made.
If a device is still holding changes that have not reached the server, it stays signed in however long it has been idle.
The reason is not convenience. Signing that device out would strand the work behind a login the operator may not be able to complete — they are offline, which is why the work is unsent, and signing out is entitled to clear the storage holding it. An operator who ticked twenty checks in a hold with no signal would return to find them gone, having been told nothing.
If a session stays open for this reason, the app says so. The action it calls for is to find a signal, not to report a fault.
Being signed out for inactivity says so on the sign-in page, and returns you to the page you were on. Nothing recorded is lost by a timeout.