At this time, Heap does not have the functionality to customize the default session duration length in Heap.
What is a session?
A session in Heap is a period of activity from a single user in your app or website. It can include many pageviews or events. On web, a session ends after 30 minutes of pageview inactivity from the user. On mobile, a session ends after 5 minutes of inactivity, regardless of whether the app’s background or foreground state.