You can make it the class end date or offset by a specific number of days. The students never see this, so it allows you to accept late work without having to change anything within the course.
*** IMPORTANT NOTE – Be aware, if you add dates to the module it will override any dates you set on the content items within the module. You will need to go back and update those dates if they are different from what you set at the module level. It is suggested that you set the dates on the modules first and then adjust the dates on the individual content pieces if applicable.
Students don’t see the calendar, so you don’t need to worry about adding it to the student calendar.