No it does not take long at all. For each activity on your AMCAS, you must select if you did it continuously ("weekly activity throughout"), periodically ("weekly -monthly activity throughout"), summers only/intermittent, or once.
It's not a very helpful section I wouldn't think. In addition to the hours I supplied on my AMCAS, I typically was pretty clear what kind of commitment it involved. On top of that, AMCAS enables you to submit activities for multiple timeframes, and UVM's system only pulls in one of those timeframes, the oldest. So I think you're supposed to answer your frequency based on the specific (often incomplete) timeframe of the activity that UVM shows.
In general, I was very unimpressed by the secondary. It seems low-tech and the character limit is harsh. They want you to describe any criminal offense in 500 characters (good luck with that if you had unfortunate/mitigating circumstances you want to explain). They ask for a diversity essay in 1000 characters; I find it amusing that their prompt and diversity statement for this question is about 800 characters. They require that you select a single reason you applied to their school from a drop down menu (location, reputation, curriculum, or size). You could expand further on your choice in your optional essay, but there is no other request for explanation. It seems simplistic that a prospective student would pick a school for a single factor.
There's also an apparent contradiction online. This page refers to a second essay on the 2014 supplement:
http://www.uvm.edu/medicine/admissions/?Page=suppinstructions.html#additional
I am not seeing "Question 2" anywhere on my supplement, and another area specifically states there is only one required short essay on the 2014 supplement.