Why a 24 hour reset?
The specifics of time manipulation aren't really fleshed out beyond the ability to "reset the day." Are we to take this to mean Cage's day was re-wound exactly 24 hours from the time of his alpha-death (which happens to put him at Heathrow at mid-day ish). Why 24 hours, you think? Maybe the mimics are able to set the reset-time based on the length of day on that planet?
What about when he killed the omega? Was this also a 24 hour reset? Omega-death was sunrise of the morning of the invasion, which seems like it would be coming up on 24 hours after the heli ride to London.
What if someone else were to kill an alpha during one of the many reset days (something I'd expect to happen a few times)? Would that have "stolen" the power from Cage, or do you think the ability is kept intact but separate?
One more, how does he know where to initially find Rita?
Great movie... hands down coolest aliens in a sci-fi