The Chalkeia was held in Athens on the last day of Pyanepsion; it was a festival of smiths and artisans honoring Hephaistos and Athena. The festival appears to have included a procession, and offerings made to the gods of the day, but nothing more specific is known about the proceedings. The Chalkeia was also the occasion for setting up the loom on which the peplos was woven that would be presented to Athena on the Panathenaia. (Parke 93)
Although the Chalkeia need not necessarily be associated with the autumn, I think it works well for those of us in the northern hemisphere that it takes place right before winter, when many of us turn inward, spending more time indoors and occupying ourselves with different crafts and arts; the winter is especially a traditional time for doing fiber crafts such as spinning, weaving, knitting and crochet–and thus an excellent time to work on that peplos!
A PDF version of the ritual script is available here.
Parke, H.W. Festivals of the Athenians. Thames and Hudson: London, 1977.