Void can view localized areas of what he wants to see. With him towering over multiple parallel universes and only being able to fit the image of Sonic and Flash in one circle, then an entire landscape later, this much is clear. So even if it shows galaxies in others, what is visible isn't the limit of his scope.
Since we see Saitama can see Void's swords, + we see Void's
swords are making the attacks, this scene where there are
seven simultaneous slashes makes no sense. The application of the swords contradicts any possible explanation unless he can swing out shockwave slices.
But we see Void can casually interact with space. His pulling space
over himself like a blanket not only moved the amount of space visible to the eye but any/all space deeper than the surface of what we could see. Blast also
observed he can only go to the higher dimension when he weaves his hand signs, which wasn't done in this case. That sounds like
Higher-Dimensional Existence. That also suggests he can access higher-D abilities without needing to be in the actual higher-D space.
As far as the speed, idk. I strongly believe that the view Void has in his ball is the actual position in space from which his attack will come, effectively skipping any distance in space and acting like a portal attack. You can see
here that his localized view of space is above the clouds, and Saitama, seeing his attacks come like twinkles in the sky, implies an incoming object, not an object that literally appears throughout all of space. We can see
here when God
approaches Garou that his movements are just weird clouds to everyone else. But those clouds are literally his feet portalling out of nowhere. This also means that if his ability is like Void's, God was walking on this Earth's bubble.
There's also the fact that Saitama pulling Void back into the universe returned him and his swords to normal size as they passed that spatial boundary, instead of immediately power-slamming the whole universe. He might just have really fancy spatial manipulation, idk.