Hi Breton, that is a handsome plant, despite the fact that it needs a good prune. I personally would prune any time I thought it needed it, but I'm sure others would have views on this. Also, I would just prune as I would any tree, taking away crossing over branches, thin top shoots, and anything that is stopping light and air from getting 'into' the tree. I would aim all the time for a symmetrical look. I am talking about pruning a tree in general, not particularly a jade. I hope you get lots more help.

I also pruned when some wouldn't recommended...(doesn't mean I am right!) - did it since there wasn't enough space to keep them all by windows (they ended up in basement anyway).
Here is one example - only trunk was left, everything is new growth (chopped in Dec.2014):

Next one chopped. It was given to me with most branches and leaves falling off - it was left on a balcony for too long; I left only few leaves - photo is about month after:

This is today's photo of the same plant. It still needs some more work, will do that probably in May:
(I am also in cold country, almost 1hr north from Toronto).
These are overwintering in the basement, temps. about 15C, with help of supplementary lighting.
Rina

If it was mine, I'd wait until mid June. Being in full sun while growing new leaves will keep the growth more compact.