(Please note that all course lectures are pre-recorded, so you can watch them at your own convenience. There is no need to "come to class" at a particular time of day.)
You can see the start date of a course from its About page. Click on the course name from lagunita.stanford.edu/courses to get to the About page. Then look on the right side of the page to learn more about the course schedule. For example, these are the start and end dates for the Open Knowledge course:
The Class Start date tells you when the course materials will become available. The Class End date tells you when the class officially ends. After this date, you will still be able to register for the course and see all of the materials, but it will no longer be possible to earn a Statement of Accomplishment.
If you enroll in a course before it begins, you will not be able to get in until the Class Start date. You will receive an email welcoming you into the course when it becomes available.