The only way to learn how to meditate is by actually meditating, so the home practice between lessons is by far the most important element of this course. If you simply go through each lesson without practicing the mindfulness meditations in between, you'll be very limited in what you get out of this program.
Each week the home practice consists of a primary mindfulness meditation, generally lasting between 10-20 minutes (with the option to try longer meditations if you wish) that you'll be doing every day. There are also usually one or two other shorter and less formal mindfulness practices.
I can't emphasize enough the importance of doing the meditations on a regular (preferably daily) basis. Like any new skill and habit you're trying to develop, consistent practice is key. If you're learning to play guitar and barely practice between lessons, your progress is going to be very slow. The same is true of this course. In order for you to get the most out of it you need to practice mindfulness every day, which you can do without formal meditation, but try not to miss more than a day or two of meditating a week.
If you don't have a chance to practice the mindfulness meditations between lessons, you won't be able to do the more advanced meditations. It's much better to take a couple of weeks between lessons to ensure you have time to practice the meditations from the previous lesson, than it is to move on to the next lesson before you've had the chance to do those meditations a number of times.
In order to make it easier to find the time do the mindfulness meditations every day, I'll try to provide a ten-minute version of the weekly meditation practice, and in some cases a five-minute version. Once you get in the habit of meditating every day, it does not have to require much of a time commitment at all. While it's great if you can spend 20 minutes meditating a day, it's much more important that you meditate frequently than for a long period of time.