Just watched it and had an interesting thought. In the kitchen 'fight' scene with Logan, Charles, Erik and Quiksilver, the latter puts on his headphones before he does his running really fast stuff. Now, wouldn't he be going faster than whatever he's listening to? Or does his body create some kind of bubble of time around him that keeps anything in that close of proximity to him going at the same speed he is.
I don't know if there is a definitive answer to this but it's a fun thing to think about.