I know this to not be true because we all exist in every dimensional plane on some level as the quantum particles that make us up bounce in and out of them. So, my theory is that Hiro halts the motion of particles, perhaps throughout the universe, but also perhaps localized as well. He does this by exerting a kind of telekinetic pressure on the universe.

To avoid getting too wordy here just understand that space-time is a limited system, though extremely immense, the area past the edge of expansion is litterally “less” than space. So, because it is a closed system, Hiro doesn’t have to telekinetically hold everything in place. He simply has to provide a small amount of pressure in this higher dimension and it will equally distribute to all places.

Think of the Tony the Tiger Diver and Bernoulli’s principle to gain an understanding of how that works. Squeeze the bottle and the diver sinks, let go and the diver floats. The reason for this is because the pressure you apply to the outside of the bottle hits the fluid inside and directs the pressure to all sides of the diver. As the pressure increases, the density increases, and the pressure on the diver forces him to stay stuck at the bottom of the bottle until the pressure is released.

So, my assumption here, is that Daphney has a kind of atomic viscosity which allows her to move at those speeds without tearing her skin off her bones. When Hiro exerts this dimensional pressure she no longer can move at the same rate because of the “dimensional friction” he is imparting through his ability. For her this would be very much like it is when you run into a body of water. You’re running at top speed no trouble then you hit the water and it becomes harder to move your legs forward. This is due to the increase in the density of the substance you are moving through. Water is more dense than air and stopped time is more “dense” than normal flow time.