First, at the moment only in 1080p and higher.
Below 1080p, f.e. 720p or 576 and 420p do not work.
But it is possible, that an Update will correct that.
So go to the system, and set your display to 1080p 60 or 50Hz (choose the best for your tv)
And then switch 24Hz Option to ON.
So it will switch to 24Hz, if a movie has it and is minimum 1080p.