If you have set a time limit on your quiz, you can grant access for extra time. If the student hasn't taken the quiz, the extra time will be added to the student's initial attempt and additional attempts.

The following Canvas Community page explains how to extend time on a quiz: https://community.canvaslms.com/t5/Instructor-Guide/Once-I-publish-a-timed-quiz-how-can-I-give-my-students-extra/ta-p/999