I think that it is too early for Twentieth Century Fox to schedule a release date for Fantastic Four II.I feel this way because the movie is not slated to premiere for another two years. There are a number of things that could happen over the course of two years that could affect the premiere or release date.
No, I do not think it's too early for Twentieth Century Fox to schedule a release date for "Fantastic Four II" when "Fantastic Four" isn't slated to premiere until June, 2015, because it is okay for a production company that wants to make money to create a long term plan. Star Wars is also a trilogy.
No, I think Twentieth Century Fox can do whatever they want. Scheduling a release date for a movie isn't that huge of a deal anyway. They can just as easily unschedule it if Fantastic Four ends up flopping in the box office. It really does not matter what they do either way.
I do not believe it is too early for Twentieth Century Fox to schedule a release date for Fantastic Four II when Fantastic Four hasn't even premiered. This is how Hollywood operates, especially if they find dates to be important. Scheduling this now is no guarantee that the film will actually be made, it's just holding a spot for it, come release time.