All Petrolessons courses are entirely on-demand. What does this mean? First, it means that there is no official "start date" to the course. Once you enroll you can go ahead and start learning whenever, wherever at your own pace. Second, it means that there is no "end date" or "date of expiration." Once you enroll your access to the course NEVER expires and you can view the course for as long as you like and as often as you like.