I have to agree with Humayun. Take your darks at the end of your imaging run. ICNR off. Have a library set of different dark exposure time, ambient temp and ISO settings. Once you have gathered enough darks from various temp, expo, iso, all you have to do is measure the first light frame temp to the last of the particular image you are taking then average the image temp.
example: first light frame of M42 measured at 10 degrees
last light frame of M42 measured at 8 degrees.
Averaging 10 from 8 = 9 degrees.
grab a 9 degree dark set at the same expo & iso time. load everything up in Deepskystacker and let it do its job. It works everytime.
Don't worry about ICNR unless it "works" for you. I know it didnt for me. Save the explanation and research about the differences between hot pixels, darks and go all nitty gritty on it etc etc. It is not required to learn the fundamentals behind it if it doesnt work for you. test it out for yourself first.
Your library of each different dark set should consist of 10 or more dark frames (20 will be better) and have an average of those 10 dark frames which you use to subtract from your light frame. Hope that explains it .
cheers