Anytime is good if you live in the Arctic. Otherwise you are fooling with botulism.
You can get away with very small batches if the weather cools, like late evening or some nights but I myself, start late October and run through March. You cannot let it stand around while you are mucking about.
After it is spiced, it should be covered with a dish towel and let set in a cool spot over night to allow the spices to do their thing. If you stuff it right after spicing, you loose alot of flavour.
Of course, if you load it with sodium and cancer inducing nitrates and nitrites, you can extend the season. I first stuck my hand in sausage making about 70 years ago. Family tradition. We never used chemicals or poisons. Commercial kielbasa often has MSG in it.
If you need a filler, use powdered milk.
BTW: Garlic looses its flavour when the sausage is frozen.
Many ethnic groups have their dominant cancer. Polish have stomach cancer. Why? Because of the afore mentioned additives. Me? I already had a stroke, so I'm not pushing the envelope, except for an angry husband here and there.