Khaleeja

As title says this question has been asked a lots of times but never clarified to the point I want. As I understood the process of subtracting calibration frames, I don't know if the master is just the sum or average frames, or for example on the flat master has already removed the dark flat and bias inside. I'm doing a second session on M42 to gather more light. It's cold outside like 0-3C° so yesterday I took lights frames at 12C° with unmdded 7D and after took darks resulted on 2C°. Today I'm using the same exact settings and this time I started taking darks as the camera was still warm from indoor and cooled just to 7C° before doing lights frames. Once it started collecting data the temperature average to 12C°. Nice trick to collect darks at the same temperature of the lights with uncooled camera. Now I'll be using the new dark and mix the two sessions of lights. The Flats should be the same. I hope. Let's say I'll do also another session tomorrow because of trees in the way and impossibility to collect multiple hours. Then can I import on Deep Sky Stacker just two random lights, all the new darks and bias and create new master dark, so once third session is terminated I'll just import all lights frames and master flat and master dark, or do I really need to import all masters, dark, bias, flat, dark flat? Thanks.