The default settings for each course in Canvas allow students to view a course prior to the scheduled start date. If you would like to keep those early-bird students from beginning work in your course prior to the start of the term, follow these instructions:

Inside your course, go to Settings in the course menu.
Check the boxes for:
- Students can only participate in the course between these dates
- Restrict students from viewing this course after end date
- Restrict students from viewing this course before start date
Select Update Course Details at the bottom of the page.

Video for a demonstration of how to enter these settings

Ultimately, you have the absolute final say on when your course if visible with the Publish button. Students can never view unpublished content or unpublished courses but if you use that to manage access to your course, make sure you publish so it is available when it is scheduled to begin!