Increased perception might make it seem to the user like time slows down.
If you've ever fallen or been in an accident, there is a sense of time slowing that's caused by being so "in the moment."
I agree , concentration can make you see more accurately what is happening , that gives you the feeling that time slows down.
Adrenaline helps to concentrate yourself to a point where you have the feeling that time slows down.
That's why you have that feeling in an accident.
That's why Roger Federer , Michael schumacher and Xavier De Le Rue are the best in their sports , they are masters of that state of concentration (and adrenaline addicts) that a normal human almost never felt.
So , it's plausible that Neji has that feeling in your video , but that wouldn't be a Byakugan ability.
Just for clarification , in our world , when you begin moving (you change your speed) , you make a distorsion in the space/time structure around yourself.
When your speed goes up , time slows down for you.
Everybody has the ability to slow down time for himself in our world.
Maybe also in Narutoverse , but that's not a Byakugan ability.