Currently, Canvas allows to assign two different time periods to schedule a quiz for two different students. However, it does not allow to assign two time limits for two different students. In such a case, we need to create two separate quizzes with two different time limits. This is a very inconvenience situation and also makes very difficult to track the grades. Assume that we have students in one class that need 50% or 100% extra time as their accommodation. For each quiz, three quizzes should be created, and in the grade area, three columns show one quiz. 
Also, Canvas allows to assign different points for different questions in one quiz, but it does not allow time limit for each question. So, if we would like to have 10 questions that each question needs different time limit, we need to create 10 separate quizzes. I am sorry, but this shows Canvas as a disable software.