You can set a time limit in HH:MM:SS format to limit the amount of time students have to complete the quiz.

Add a time limit to a quiz

• Within a quiz, click the Settings tab.
• In the Time Limit section, add the desired quiz time.
• Save the quiz when complete.

 Quizzes with a time limit will display a countdown timer for students as they progress through the questions:

• If the timer runs out, the student's quiz is automatically submitted and any unanswered questions are marked as incorrect.
• Students will see the Passed results page if:
  • They earn a passing score even if the time expired, or
  • They earn a passing score after their answers are manually graded
• Students will see the Failed results page if: 
  • They earned a failing score after the time expired, or
  • They earned a failing score after their answers are manually graded, or
  • They didn't answer enough automatically graded questions correctly even if the quiz requires additional manual grading
• Students will see the Requires Grading results page if:
  • The time limit has expired and there are questions that require manual grading to determine their score
• Every quiz results page will outline the number of questions that were answered along with the elapsed time. 
• Quizzes with time limits will show the applicable time limit on your Analytics > Quizzes page

For more information on Quizzes, view this article.