I'll always want the sheet metal and the body filler to be at a minimum of 65 degrees F constantly. I've had good success with that. That means working in a heated garage. You will experience failure with your body work if the temp is not consistant and gets real cold and then hot and cold and hot etc. The filler wil not stick to the metal. So if you're in an unheated garage, it's better to wait 'till spring time to do your body work.