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Yes thats right. Even in dark skies images should always be fully calibrated, that is, with darks, flats and bias frames. Any in camera noise reduction MUST be turned off also, including high ISO NR, otherwise it may interfere with the dark subtraction process. In other words we need raw data straight off the sensor with as little manipulation by the camera as possible, thus allowing the software to properly calibrate the images.
I find 10 minute subs is the sweet spot for me on averatge temperature nights. I once tried 3x30 minute subs on the Helix Nebula, but found thermal noise resulted in a noiser image than 9x10 mins. 5 minute subs also gives a slightly noisier total, however on very hot nights 5 mins is actually better
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