Cold nights = clear = freezing my ass off waiting for canON to noise reduction for 11minutes
Turn the Long exposure (dark frame subtraction) noise reduction off. Then at your convenience, in between taking pictures or walking back to the car etc, put the lens cap on minimise the aperture keep the end dark and take your dark frame(s).When you get home subtract the darkframe in photoshop, simplez. I wish the camera would show you the image captured whilst its doing the dark frame NR at least then you would know if it was worth waiting for (does anyone have a camera that does that?), but yeah I just do it manually these days, saves waiting inbetween shots.
(if my reply makes no sense look how "dark frame subtraction" (which is what is used for the long exposure noise reduction) is done and it should be apparent how you can do it manually as long as you know how to add the dark frame as a layer in photoshop/gimp then subtract it).