Yes. You can start and stop when ever you desire. You can interrupt the test at any time and come back later to finish. To do this, click on the "Stop and Restart/Resume Later" button on the bottom right of the page. This will allow the system to save your test for your return visit. When you wish to return, login, select "Restart/Resume and Continue an Unfinished Test" from the Welcome page and then proceed to the test.