Animations, many system events and behaviors are automatically adjusting their speed to fps, they are already using dt for this.
Same animation on 60fps and 30fps PCs should take the same time (ideally), "Every 1 second" event should take 1 second, bullet with speed 1000 will cover 1000px etc.
If your second PC is so slow and laggy that C2 engine can't compensate it, then you will not be able to do this with dt either.
Normally you only need to use dt when you are controlling objects with events, like moving a sprite every x pixels every tick, or scaling/scrolling the view.
Edit: I did some testing, looks like dt can't be bigger than 0.0333. So if fps is below 30, the dt will still be 0.0333 and the game will run slow. You can't fix this with dt, because the actual frame duration is longer than 0.033
Maybe you can do this by getting system time with JS or some addon..