It would seem it is possible to change the session time
How long does a session last?
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.
As far as changing it to "50 minutes" I don't know if the options provide that level of granularity. Have you tried?