You have access to the course and its contents from the published start date through the published end date plus 30 days. This gives you time to finalize communication with the instructor. There are no extensions and there is no way to access the content or personal work beyond those dates.
Please note that your instructor will likely NOT be monitoring the discussions or any submissions you make after the class end date. Please check the course syllabus for due dates and submission acceptance policies.
The online lectures cannot be saved to your own system for use in the future. Please make sure you preserve a copy of any work you submit prior to the end date.