You can interrupt a course at any time, return later even on a different day, and resume where you left off. Unlike some other vendors we do not discard your work overnight. You can even interrupt a quiz, just click on "Finish" to save your work and when you are ready you can return and restart the quiz.  When you click "Submit All and Finish" the quiz will be saved and graded, at that point you would need to start any attempt is you were not satisfied with your score.