I believe that we should do both. 1 second can lead to the ball being called as held even if it is just rolling through the positions of several robots. I believe that 3 seconds would be a good time.
For the distance: I think that the distance should be decreased to half the current distance. For reference: 1.5 m is the diameter of the center circle in KidSize. A group of robots can clearly not be considered holding the ball if they are this far away from it.