Your temps are at the low end for liquid feeding, any cooler, and it's probably too cold for them to take it. The bigger question in my mind is how much honey/stored syrup do they need to overwinter in your area? Another thing to consider is whether they are still rearing brood, and if you want to be sure they still have space to do so. I would feed until they are as full as you want them, unless it gets too cold first. That's what I'm doing right now with my hives.