Kurkistan, the main problem I have with both your engines is that Brandon has specifically said that Allomancy has FTL built into it, and my understanding of relativistic physics is that that means going from point A to point B without crossing the intervening points. No matter how fast you accelerate, you can't exceed the speed of light via normal travel.
ulyssessword, I agree that an object is either entirely in or entirely out of a bubble. However, what defines an object? Are two rocks tied together 1 object, or three? (2 rocks + 1 rope). If they are three objects, then you still have to deal with interactions between the two "time zones". If they are one object, then what makes them one object? I think that an "object" is defined in the Cognitive Realm, but that's just a theory.