Days are still 6 hours or 24 hours in setup, when I increase the size and slow down rotation those values are still used to calculate days, By KSP's logic with DayLengthMultiplier set to x2 Kerbin takes two days to turn once on its axis, not a deal breaker (still my favorite mod for breathing new life into the game) but it does look odd.
I'm not even sure if that logic is accessible, just a thought.