Can I ferment black garlic intermittently?
YES. Yes, you can. I just did.

My first attempt in my rice cooker had uncovered garlic heads in it for 10 continuous days-- the result was black but dried hard as rocks (and the process stank up the entire house the whole time).

My second attempt involved wrapping each head in two layers of foil, then putting the garlic in a much lower temperature warming oven (no thermostat at all, just a light bulb) for 10 days, which resulted in beige garlic. I then switched it over to the rice cooker for 2 days, turned it off, checked them, then another 2 days, turned it off, forgot about it for a day, checked them... another 2 days, turned it off, checked them... and found DELICIOUSNESS.

It needs more time, I think, it's not as sweet as I'd like yet and could be a little darker. I've seen some Koreans mention finishing the batch by just hanging the garlic in a bag for a week, so that's what I'm going to do.