You can add accommodations for a student in New Quizzes. Accommodation settings include adding or removing time for all assessment attempts, and multiplying time limits by a set multiplier.

Accommodations apply to all assessments in a course for a student and only one accommodation can be set per student. Set accommodations can be viewed in the Accommodations column and in the Moderate panel.  

To manage timer settings for a single attempt, you can moderate a student's assessment attempt. Moderating an assessment attempt will apply any moderation settings on top of any set accommodations.

Note: Quiz availability dates still apply when moderating a quiz. If the Until date passes before a student completes an extra attempt or extended-time quiz, any in-progress quizzes auto-submit and the quiz closes, even if the student's attempt has not expired.