Whenever you're ready! The lessons are available online any time, and your access to the class never expires.
This is primarily a design class meant for experienced knitters who want to start making custom garments. If you want to learn to knit, you should take one of Craftsy's many beginner classes and work your way up to this one!
As long as you need! Your access never expires, so you can come back again and again.
Ask your questions on the platform and you'll receive instructor feedback. Your fellow students are also likely to jump in and offer advice from their experiences.