Spring 2020 has revealed a major flaw in the design of how Canvas provides extended time for students with disabilities. Following Canvas's own instructions for providing extra time on quizzes will not, in fact,give extra time for a student if the Quiz Availability has been set to match the time of the Quiz. Adding to the confusion, the student will show in the Quiz Moderation view as having received extra time. Many instructors set the Quiz Availability to, for example, 10:30 - 11:00 am, to match the 30-minute time limit. However, this setting overrides everything, despite the universal understanding that giving specific students extended time extends the quiz availability for them.
There are two time-related elements for every quiz: "Time" and "Availability." Canvas needs to make a very large alert/warning as soon as someone begins to type into the Availability settings window AND in the Quiz Moderation window to explain that if Instructors set the Availability of a Quiz to match the Time, no student can receive extended time on that quiz.
Our suggestions on our campus are to either: 1. create a separate availability for students who require extended time accommodations, with the availability window including the extended time, or 2. make the availability window of the quiz long enough to include any accommodations (a best practice in these difficult times of everyone working/learning from home).