Hello Cynthia Young!
It depends upon the type of course to know when activities are due. The best way to know definitively would be to work with the course provider. However, if you do look at the calendar you should see due dates for courses that have due dates. These due dates could have been selected by the course provider or are automatically generated based upon how much time your student has to complete the course.
Blackout dates are dates that are supposed to be skipped when automatically generating due dates for activities. For example, a course provider could specify a holiday, weekend, or another recognized day as a blackout date. For these dates, activities will not be due on these dates.
I hope this helps address your questions!