I only plant them in late summer now because I grow so many other things in summer. Lot's of bean shelling, tomato canning etc to do.
I now start seed inside in July (because of our heat) . I plant them out late August/early September and they will grow all winter. When I cook a batch to eat I do enough to freeze a couple meals too. They warm over wonderfully.
About every 3 years I save seed. You can put them in the freezer and they keep many years. I saved seed last year. I always save seed from the 3-5 plants that grew the best through the winter. I've done this many years now and I feel like it helps with hardiness and health of the plants.
In the beginning I planted them in spring. By the following spring they could easily be 3-4 ft tall! They grow amazingly well.
I do think those in the coldest areas could benefit by planting in spring. But experimenting is always good!
I had 5-6 years old collard seeds. as I didn't expect them to germinate and I put a handful of them in a flower pot. I think all of them germinated but made a big mess. I could not separate them (only 2-3) to transplant them so I fed my chickens. those 2-3 I transplanted.