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Ivan, all this really depends on focal length employed. By way of example I use 90 seconds per channel on Mars at 12700mm focal length. That gets me roughly 4300 frames in red, 3200 in green and 2800 in blue. If I used a smaller focal length I would only need to go around 60 seconds per channel to get similar results. However using the largest focal length v the amount of frames required is the question you need to answer.
With Saturn the issue is more prominent. I am using the same focal length at present and going 2 minutes for red, 3 minutes for green and 3.5 minutes for blue. This gives me a large image scale to start with, that gives good detail on the rings but blurs out detail on the planet. For better detail on the planet I need to use a much shorter focal length to gain as many frames in a shorter time frame. It is a choice related issue and when seeing is not great I choose to go for ring detail.
Now to more directly answer your question, you can go 4 minutes at modest focal lengths in each channel on RGB for Mars. Its day is slightly longer than ours so it rotates slower. At very high focal lengths up near 18 meters this time would need to be a bit shorter to accommodate rotational blue. You would need to do the Mars to work that out though.
Saturn though, does require shorter runs to capture spots etc ont he surface. 2 minutes for all colours in RGB would seem to be the maximum. That means adjustment to focal length and getting that down near 6-7 meters will give sufficient size and frame rates to get frames for smooth images.
Remember this is just like any photography, the available light determines the exposure, the faster the exposure the less blurring that can occur.
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