Or: How long can you go before turning the heat on?
Ideally, we could weight your date-of-first-turning-heat-on by
plant zone, to account for regional differences. And clearly, there are some advantages to be had by people with new, well-insulated homes, and some disadvantages to living with young or old people, who may suffer more from unreasonably un-heated homes. My feet are kind of numb right now, but there's nobody else to whine about it.
I'm pretty sure I can make it at least to November before turning heat on.