Yes you can log in at any time over the several weeks the class runs for.
All the class material is downloadable, so you could even just get the material and work through it later. The only thing you lose in that case is the chance to ask questions from the teacher, that's possible only during the four or so weeks of the class. During the class weeks, you can post questions on the class message board at any time (and read other people's questions and their answers, and chitchat with them if you like), and the teacher comes in and answers questions every so often. Some people upload images of their class-related work, although for an EQ class that might not be so interesting.
I did only one class with them (Hawaiian Applique 101) and the printed material was super clear. I've heard good things about their dyeing courses as well, but don't know anyone who's done their EQ.
I still think a good book comes cheaper in the end... But I'm good at self-teaching and don't really need individualised teacher input so much.
Good luck! and let us know how it turns out if you decide to take the class.