I think if you were posted from mid/late Oct to mid/late Nov, with a deadline in mid Oct, most folks would hopefully by done before November and Nano anyhow, wouldn't they? Pinch-hitters might get hit, but not everyone does Nano anyhow. Alternatively start at the end of Sept and finish with Halloween. I like the idea of a Halloween/autumn fest, that starts with Mabon (Sept 21) and continues through. Halloween's the end of the pagan year, and a highly magical time, one we know was a festival in HP canon, and there's the autumn harvest plus the encroaching winter to play with, seasonally.