Not doable while school is in session by many if not most people, assuming they want to pass their classes.
But what about during summers? Over spring break? Christmas?
Definitely doable over the summer after first year. Many people do a summer research project, and funding is available for medical students to do this. Not doable after that--you'll be studying for Step 1 in the summer after second year, and finishing your rotations in the summer after third year.
You could probably work over your shorter breaks, but if you're studying properly during the semester, you almost certainly won't want to spend your week off at a job.
How about a couple of evenings a week?
A few afternoons?
Depends on the student and the job. I taught for Kaplan during my first year and a half, but I was doing that all along (i.e., before starting med school). I would not advise anyone to start teaching for the first time *after* starting medical school. I've also done some consulting type work, which I was able to do more or less on my own schedule. Since you have a law degree, you may be able to do something similar.
Is working during medical school always a bad idea?
I'd advise against it during your first semester or block. You don't know how intense the workload is going to be, and you really don't want to flunk your first set of classes because you didn't put enough time into studying. If you find that you have a lot of time and you're doing well in school, and you find a job that is commensurate with your schedule, then sure, go for it.
Realize, though, that the vast majority of medical students do *not* work during medical school. Chances are that you will not be able to do so, and you should absolutely not count on that income.