hehe, s'all good lazy.
The way I "think" it will likely work:
Bullettime only slows down a radius. Let's say 100 meters. Everything within 100 meters of you slows down when you activate it, but you (and, as I said, your teammates if you have a high skill level) retain a better speed and rate of fire while slowed down, while your enemies that fall within that radius do not.
Naturally, this would mean that anyone outside of that radius, whatever dimensions it may be, would see you all slowed down. The only way around this that I can think of off-hand is that whenever a bullettime is activated, the radius of the bullet-time is somehow "shielded" from the outside world. Like an impenetrable force field that cannot be shot into (maybe you can shoot out of it, though, increasing it's advantage), or that none of the beings or objects within that radius can be seen by the outside world for the duration of the effect.
Basically, there's no way they'll allow BT to slow down the entire world. That would be annoying and painful to everyone else, and it would happen constantly. So in effect BT will not make you faster, it will literally make you SLOWER in comparison to the outside world, but it will give you the advantages that BT would offer within the dimensions of it's area of effect.