The way I see it:
in order to keep the original idea of continuity, they'd have to make the FF two years older then they are now, since ca. 1 year has passed in the ultimate universe so far, and they were suppossedly created 1 year before spiderman. That would mean we'd get a HUGE gap in their personal story. We'd get something like "two years have passed, and we still don't know how Ben could get altered the way he is" or stuff like that. That doenn't make sence for me. Therefore, I'd actually like to assume the "Nevada today" is to be taken literally, that the FF have been formed right around the time Peter was busy with Black Cat, Doc Ock or Carnage, right around the time the X-Men were busy solving a conspiracy in Washington D.C., right around the time the Ultimates sat around, complaining about yet another lack of important missions.
All prior mentionings of the FF (as in Ultimates#2) would have to be ignored, and they wouldn't even EXIST except for the thrice damned Team-Ups.