Your course's request due date is the date by which companies must apply to your course. After this date, you will not receive any further requests and companies will no longer be able to apply to your course.
Change your company application deadline by going to the settings tab on your course page. Your submission deadline cannot come after your course start date, so you may need to edit that as well. To do this, click the edit icon, with the pencil, on the course page to make revisions.