Computing Session Length from Raw Data

I want to compute session length from our raw data exports - similar to what the Unity Dashboards report for "Total Daily Play Time Per Active User", but computed on our end (via BigQuery) so we can histogram it.

We want to match what the analytics dashboard is doing for calculation to avoid discrepancies. Can you explain which fields of which exports the users "Total Daily Play Time Per Active User" is computed from? Obviously every event has a timestamp (but this doesn't allow us to tell when they were/weren't using the app in between timestamps.) AppRunning has a "duration" parameter, but there doesn't seem to be any documentation on when/how AppRunning events are sent, and if we can assume one is sent when the app is killed / sent to background etc.

Any advice on how to replicate this calculation would be appreciated.

 

Suspect duplicate of https://forum.unity.com/threads/how-to-get-total-playtime-from-the-api.446206/. Will update if that doesn't cover it.