The system has an autosave feature that is activated shortly after you begin working on an application. Consequently, if you fail to save your work and are timed-out of the system, you may only lose the work you entered between the time the system last saved automatically and when you were timed-out.

That feature notwithstanding, you are encouraged to save your work frequently. On the last screen or application page there are two buttons. One button says Save for Later, the other says Submit. If you click on the button that says Save for Later your work will be saved. As long as the recruitment is still open, you will be able to submit your application for consideration. 

If the position closes and you have not submitted your application, you've lost your opportunity to be considered an applicant. You have not applied for a job until you click Submit.