It is not necessary to add due dates to assignments. It is optional feature. To add due dates to the assignments, use the scheduling Assignment Scheduling Tool.
1. Start at the Course Home
2. Locate the assignment you want to add a due date to.
3. From the Quiz page, clock the clock icon in the top right corner.
4. In Assignment Settings, locate the Available to Students Until section to add a due date.
5. Click Save