There are a few different schools of thought on changing time, and personally, I subscribe to a theory more like what Carrion proposes if time travel
is ever possible. Every choice is a branching-off point for a different timeline.
That having been said, let's say that perhaps the Nazis did create a time travel machine and were successful. We'd never know it either way. There
would be no record of them having altered the timeline, because there would be no record of what had happened differently before they changed the
timeline.
It could also create a series of paradoxes for each and every event they changed. If they are successful in changing an event and it leads to a
favorable outcome, they wouldn't know to go back in time to change it in the first place, unless it is always the same person, who has removed
himself from any other responsibilities in the war.
I'm skeptical that they did develop time travel, but I'd be surprised if at some point in our future it wasn't attempted by someone who wanted the
Nazis to win. We'd never know it however, as our lives would be changed (if any of us even existed as we do now) to reflect the changes to the
timeline.
Anyone have a headache pondering the possibilities now?