Hi @ggillombardo
This can be challenging to new Canvas users, and one I spend some time on explaining to my own faculty - Canvas Modules are used to control how course content is displayed to students. So regardless of many of their own settings, Module contents' availability and even visibility is determined by the settings for the module that content is in.
So, as both stefaniesanders and @Robbie_Grant have said; while your assignment might have availability dates set, those dates do not matter if that assignment is located in a module that is unavailable. Below is an example.........
I have a module that is locked until Thursday............

I have an assignment In that module that became available yesterday..........

As a student I will see that the Module and the assignment are grayed-out and unavailable on the Modules page.....................

And, if as a student I try to access the assignment from the Assignments page, I will get this message - the same message your students are getting..............

I hope this helps clarify,
Kelley
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.