Let's put the basics down : An event is set at a point of IG time, and kills the PCs. The PCs then "go back in time" (no duplication of the PCs), and have to alter the course of time to avoid the event. If they fail, the loop triggers again.
I'm not just speaking theoretically here; I've run games where that kind of "rediscovering what we already know" thing happens, and we gloss over it as fast as possible. Which pulls the teeth out of the tactical tension you're hoping for with this choice.
@Saffron I would be using some system that has means to measure time with some in-game timer. The first thing coming to my mind is how, in Psi*Run, the characters are chased by the opposition and need to move faster than the chasers. In your case, the chasing entity could be time.