You cannot change the default session timeout duration in Google Analytics.
A session is a group of interactions that take place on your website within a given time frame. By default, a session lasts until there’s 30 minutes of inactivity, but you can adjust this length so a session lasts a few seconds or several hours. A session can be as short as a few seconds or as long as several hours. A single user can open multiple sessions.
Read more here: https://support.google.com/analytics/answer/2731565