If user have chosen Remember me option timeout is 14 days. If not, timeout is 1 hour. You can change it by changing SESSION_LIFETIME value in init.php. It represents a number of seconds that will be set for a valid session without a refresh. Look for this:
define('SESSION_LIFETIME', 3600);
And set to any value you like. It needs to be a number.
If so, is this configurable?
If so, how?