Ketut,
If you are asking about how many subframes, Just because of time factors, you almost always take more dark and bias frames to build your masters than your flat frames. For example, because I can do the darks and bias at home, I shoot 100 dark subs and 400 bias subs to build my masters. For flats, since they are taken in the filed, I take 25 or 36, depending on how much time i have available.
If you are asking about how long the frames should be time wise, your darks should be at least as long as your light frames, and if you are doing scaling, some argue they should be up to 5 times as long. Flats, on the other hand, are much shorter, typically under 10 seconds, just long enough to get to around 32,000 counts in the brightest section of the flat frame.
Hope that helps.
Best,
Jim
