That is correct. If a student starts a quiz with less time remaining before the quiz closes (until date) than what you set in the allowed time to complete a quiz, it will be auto-submitted when the until date/time has expired before the student can complete the work. Please see the following section in a student guide concerning quizzes 'View Time Restriction Warning'. If you set the due date to the same as the until date, the submission will not be marked as late when auto-submitted.