It's not a bad theory. I like the way it does change the opening scene.
In saying that, it lacks the credibility of simplicity. Eb could have given himself an alibi in 10 different ways. Why use something as dangerous as time travel? Not to mention, Vadderung says that once an event has "occurred" (whatever the hell that means - even Jim acknowledges time isn't linear) it has a tendency to try and occur exactly the same way each "time" it repeats. It then apparently requires an enormous amount of energy, will, skill and a measure of simple luck to overcome. Seems like Eb wouldn't bother over an alibi.
My theory is that because there was an event we shall call "Creation" that separated it from non-being/chaos(?) by the Creator being, there was originally only the one universe and time was born. It then followed a sort-of linear form from the perspective of someone inside the timeline. However, at some point divergent timelines happened and so things get more confusing and we get a multiverse system. How and when and indeed why these divergences first occurred is unknown, but I'd bet money it was to do with Free Will and quite possibly around the point Lucifer rebelled.
From the Outside of Creation, future and past are terms that have no meaning because it would appear that all events were occurring at once. It would be the sheer act of actually measuring (i.e. visiting or viewing) that would actually make an event more or less 'real' (for want of a better term). But I guess in order for things in a universe to have a before and after, there must be a sort of 'beat' of the universe that keeps ticking along and would have done since it's beginning. But we are getting into very abstract problems here.
Whether Dresden's universe is the first or base reality (unlikely) is unknown. But I guess we might find out.
