While Canvas courses don't open until the first date of classes you are able to have your course open earlier or later if you wish. Remember you have to publish the course as well for students to be able to see it. To change the course start or end date:

1. Scroll down to the bottom of the side navigation

2. Click Settings

3. Click the calendar icon beside the start date and choose the new date

4. Scroll to the bottom of the page and click Update Course Details