I taught a couple of MCAT prep courses with EK towards the end of MS2/beginning of step 1 study time. It was a little stressful at times but was a nice break away from typical medical crap. Class was basically 8 hours a week, plus anywhere from 1-3 hours prepping at some point beforehand. I just reused lectures between the two classes to cut down on prep time.
I'd say it's possible for sure, but it depends on what you're doing. In my case I was replacing free time with make-some-extra-money time, so I didn't mind. If it would take away from whatever you need to do for school, though, I'd say it's probably not a great idea. Even if you did want to work, 11 hours/week was quite a chunk of time for me. Whatever you do you'll probably be pretty limited - I wouldn't think more than 20 hours/week tops - unless you're a mental machine.