I did mine in November....if its cold...prepare your cold weather attire accordingly. Take a look at the weekly forecast ahead of and past your century date. Be prepared to start riding and pull off layers if you get too hot. Make sure you can pack it away in your jersey....
And...regardless of hot or cold, you can still cramp up without a proper hydration plan. If its the night before your century and you've decided to start drinking water...........your too late.