Technically, Brotherhood has a decent amount of action in 2012, so it's not only in one time zone. And the animus can only show backwards in time, but you know that. Actually, the secret that getting all the glyph unlocks in AC2 shows a concept very much like what you talked about
*spoiler*
(Subject 16 reliving Adam and Eve's escape from Eden, in a very unexpected way.)
*spoiler*
(Subject 16 reliving Adam and Eve's escape from Eden, in a very unexpected way.)