A Session Timeout refers to how long the mParticle SDK will keep the app open in the background when a user switches apps.
iOS has a maximum background time of 120 seconds enforced by the OS (with a few exceptions for specific use cases like music playback and location tracking for directions, etc.). After that the app will be killed. Based on that, mParticle has a maximum allowable timeout of 120 seconds.
To learn more about iOS session management, please visit our docs.