Well, I made it to late November before turning on the heat in the apartment.
I came home late one night to find the place at a chilly 55 F = 13 C. That's rough. I can sleep in 60s F with my famously warm bedroom gear, but it is hard to brush one's teeth below 60 F.
Strangely, 2 days later it was a breathtaking 70 F and sunny in St Louis. One of those days where it felt like a true moral imperative to go outside. (Which I did, running around CC Lake just like the old tri days.)