Canvas privileges continuing student access to information once released. For example, an assignment cannot be unpublished once students have made submissions. Since the assignment instructions are visible on the page, this means that students can always access those instructions once a published assignment's availability date has passed.
A colleague of mine puts the details for an assignment in a separate file that is linked from the assignment instructions, and he wants to hide those files after the assignment due date. Canvas allows us to change the availability dates of individual files, so this interest can be met by scheduling the date for each file to match the associated assignment's until date. Note that the file availability date cannot be set separately for individual students, which may complicate assignments with differential due dates.
I have been teaching in a technology-mediated environment since the days of HyperCard and teach classes in history, online student success, and how to be a health care IT trainer. Every day I learn more about Canvas.