Sarah depends on what you want to sow? best to follow the packet instructions as they do vary.

I'm confused - most people do baskets in late spring, using summer bedding in baskets for summer, and maybe a winter planting done in September to go through the winter, usually with temporary plants that get binned or transferred to the garden if they're hardy. So I'm not quite sure what you mean by preparing to do them for next year...

I was confused to and thought perhaps it is about seed sowing?