While you are right here as well, they did show the fleet's impending arrival in "28 days." I thought that was a foolish thing to do as well, as it implied that the real battles were very soon. It would have been wiser for them to leave that part ambiguous.
Yeah, I had a problem with that too. Although my problem was putting the 28 days thing made it seem like they were rushing Ender's training even more instead of giving the illusion he'd been there more than a couple of weeks. It felt like that in the movie.