Adding extra time for assessments can be set specific to your students.
To do so, navigate to your course and your course roster. Select the student for whom you would like to grant additional time.
Adjust the option for Time Limit Multiplier.
The most common settings at 1.5 for time and a half, or 2 for double time.
For example, for a student who needs 3 hours for a 2 hour test, you would set their multiplier to 1.5. They will have 1.5x the 120 minute time limit to grant them 180 minutes to complete the assessment.