Generally, courses consist of about 6-10 chapters, and because typically a chapter is released each week, a course can be 6 to 10 weeks long. You will be able to see all chapters at once, however only those with the grey arrow have been activated (i.e. you can access the chapter content). You can find all the information on the start date and duration of the course on the respective course description page.
You can find all the information on the course workload on the course description page too. The workload depends on the course, as well as on how deeply you decide to go into the material.
The normal workload of a pro course lies between 12-16 hours, the suggested course length is about 4 weeks. If you don't like to spend 3-4 hours a week or would rather finish the course faster, you can do so as well. Take as little or as much time as you need and complete the course at your own pace.
Please keep in mind that the workload is just a theoretical guideline. For that reason, it is normal if your workload differs from the indicated one.