Maybe you could fake it. Say you can slow time for 5 seconds. You active the power and everything slows down for everyone but you. Everyone sees you moving extremely slow in the direction you were when you activated the power, even though you're still moving at normal speed shooting people or running around or whatever. At the end of the five seconds everyone sees everything you did happen extremely fast and everyone is at normal speed again. If the duration of the time-slowing isn't really long it would work I think.