For Security Reasons your default is set to 20 minutes of no activity and then the system will log you out.
If you choose to change your default, you are acknowledging that you take risk for leaving your system open for others.
To change the default Log Out Time please go to your Profile:
When you enter to your profile you'll see the Access option, please click on it so you can see all the options to update your Log Out Time
When you open the Access Tab please make sure to scroll down so you can see all the options you have to change the Log out settings
Once you have updated your settings for the time the system is going to wait to Log you Out, please remember to click on Set Default Time to make sure your changes are saved in your account.