My problem was mainly the availability of the materials. Codecademy and duolingo give you access to as much as you require from the start and you can go through as quickly as you like. The university driven sites limit access to so much per week (though I'm not sure how courses will operate the second time) and demand you stick to their schedule, though granted this may be due to their need to peer-review the more demanding assignments.

Unfortunately my free time isn't available in nice predetermined six-week chunks, but even if I am able to catch up three weeks or more in a weekend the courses gave a very negative vibe about continuing to progress as soon as you miss a single one of their deadlines (i.e.- "you missed our deadline for this multiple-choice computer marked test, so your effort no longer counts"). I've 'failed' several coursera sessions in the fourth or fifth week for that reason.

Timetabling seems a very traditional educational view, and it contrasted sharply with codecademy and sites like duolingo where I spent Jan and Feb learning the basics of new languages - computer and human. I finished the courses I took because I did them at my own pace.