When you sign up to a course, the course material is delivered to you via email, normally on a one-email-per-day basis so the courses allow you to learn on a day by day basis, over a set period, which can be anything from a few days to a month. It varies from course to course, but typically this will require 30 minutes of your time per day. And if you miss a day or days, you can pick up as required or as suits. You control the pace of your development. Some courses are free, some require a small initial cost to buy the course.