Analytics is the tab which reports on M/IC Usage for Events within a Project. You can explore the headline usage numbers and drill down into engagement levels with specific pieces of content.
Session length is calculated as time between subscribing to event channel and unsubscribing from event channel. Usually this translates directly into opening app and closing the app, but may differ based on the app logic, for example if the app does not activate event automatically when opened, which delays the start point of user session.
If the user disconnects and reconnects then this is considered as two different sessions, each with own length. This does not affect average sessions length calculation as duration of all sessions are added together for this calculation. Disconnection may happen due to different reasons including, but not limited to:
App being placed into background
Device going into sleep