Worried over what? Lmaol.
Dude, there is no point in this. All that matter is how well a script is brought to the screen.
Someone brought up Eragon? Well, there were fans of the book that said that the film butchered it. And sorry to tell you, the film itself wasn't that great- and do you want to know the obvious key reason behind that? They didn't translate the script (which was just okay) to screen that good. It's not that the film was PG, lol.
Time length matters, because there is a chance that they took out important character evolving scenes that are needed to tell the story the way it has to be told. This fits into adapting the page to screen. If scenes that are meant to be in the film are cut, then- that's bad.
Sending a film into the MPAA does not reflect the movie, all it does is say whether a film is PG or PG-13. Which, these days, there isn't really a difference between at all.
The only scene that we may lose is Doom killing that one security guard, that's it. But, we wouldn't even lose that entirely- it would be set up more Hitchcockian, editing around that- "what you don't see is sometimes more disturbing than what you see." Have the guard and Doom in the room, show start of action- cut out- have FF arrive and see the effects of what Doom just did, easy as that and story wise you don't lose
anything. The point is still brought across.