The length of the timeline is based on the very last marker or instrument. You can see this in action in FMOD Studio by allowing an event to play by itself. It should automatically stop after the last marker in the logic track or the last instrument on the timeline.
In the FMOD Studio application it will perform a non-immediate stop to allow reverb tails or delays to play out.
The only time an event will not stop automatically is if the “Persistent” event macro is set, or it has loops.
To check the length of an event, you can use game code to grab the actual length from the event’s description.