I think that having plenty of lead time, especially for marketing and filling the spaces in the course is helpful. I have a feeling you have a huge fan base, and may be able to fill a course with much less lead time that most organizations I work with, so you could do it earlier. I generally like to have my courses posted about 6 months in advance.
If we had an indoor space to teach, I think these temperatures are fine. It's maybe not the best time to implement permaculture on the land, but during the course we don't do that much implementing anyway. We can still make some bricks, make compost, sheet mulch, grafting, dig some swales (if you have the machinery), and more.
I don't know what else you need to do on the site. My basics for every site I teach at is that I recommend that you have these things in good, clean, solid order, and then the students will be happy:
Sleeping (This can be tents that people bring themselves, but even the spaces for the tents should be given some care. If you do tents, the course will be lower costs as well.) Showering - Clean, hot showers. Shitting - Somewhere clean and private Eating (kitchen, cooks and place to eat) Class time (comfortable place to learn)
If you have all those things, then the course works well. If even one is missing, then participants get a bit fussy.
There is a great PDC teacher or two that live at the Possibility Alliance in NE missouri, that might be willing to come down and teach. The guy's name is Adam Campbell. you could leave a message for him on his phone to see if he would be interested (660) 332-4094. But I imagine he may be quite booked up already too.
I am including Brecht and Nick in this conversation as well, as they may be interested in teaching the course. These are colleagues of mine from Surplus Permaculture Consulting. Both have lots of experience internationally and are great teachers. If I taught the course, I might want to bring one of them along to co-teach as well.
Let me know.