Shutter slower than video FPS I'm trying to shoot low light video on my RX100 m3 and I want to make the best of it. So it would make sense that the ideal setting (in many cases) would be to open the shutter for as long as it can be open for that frame.
So if recording at 25 FPS video, then you would have the shutter open 1/25 seconds. That way you get max light in.

However I notice my camera doesn't mind having the shutter way slower than that number, I guess that means that it actually spills same information onto several frames? 

If I set it to 1/25 does that mean absolute maximum. OR does the camera perhaps need a few milliseconds between each frame and therefor 1/25 for 25 fps video is too slow?
"If I set it to 1/25 (shutter speed) does that mean absolute maximum (or lowest setting)?"
Yes, if it was a non-digital video camera. This rule applied to the old non-digital (film) video cameras where you cannot set shutter speed lower than the frame rate.

Meaning that one celluloid was exposed for the full 1/25th of a second. Assuming 25fps. 

For digital video cameras each frame can be blended with the other. This technique allows you to film in low light situations at the expense of motion blur. It can be used to create what some called a dream like sequence.

You should just view this as another creative control that you have to managing low light situations or adding motion blur to your videos.

See example below: