If you mean the amount of time before the application will automatically log you out (for security purposes), this is controlled by a value in the following configuration file:
For more details, see also slides 2-6 of the following slide deck:
By default, this SHOULD be set to half an hour (i.e. 1800 seconds). However, there are some known issues from the Symfony framework with this setting. If you want to increase it, I recommend that you do not set a value higher than 4800 seconds - i.e. 80 minutes. Despite the inaccuracy, users have reported to us that this makes the automatic logout last closer to 55-70 minutes.