I have been asking the same question. I usually do two videos a day and then the little practices quizzes, but I don't think that is how I am supposed to do it... 

Yes please, I need this information!

I am looking at using this next year and was wondering the same thing. It looks like the last 4 units are all documents and videos, at least some of which are part of other lessons, so they aren't really "units".  I count 59 actual lessons. There are quizzes for every 3-4 lessons and each unit has an short test. At 3 lessons a week, that's 20 weeks.

My student (10th grade next year) has already studied a lot of this on his own (for fun) and is finishing US History now.  I will be assigning one section a week - the group of lessons with the assigned quiz, and adding the unit test at the beginning (Mondays) of the following week, before starting the next unit.  That puts us at 19 weeks, which is 4 weeks over one semester for us.  I will be allowing him to move ahead on the schedule as well.  I may have him start this one early, so we can finish before Christmas break (I'm sure he'll be thrilled).

Here's hoping that pacing goes well!  I haven't gone through this course myself, but have used other Khan Academy videos and courses.  For background, I am a homeschool mom (9 years and counting) and teach multiple grades and subjects at our co-op.