Too Soon?

I'm thinking of going to see United 93 at the cinema this weekend, and I mentioned this at work. It seems that a number of people seem to be against this film, because they think it's too soon after the real event. How soon is too soon? Would it be the same in 10 years time? Or does this put closure on a horrific event? I think I'm going to see it anyway, on the basis that I want to understand more about what happened.