The way that I recall it, they landed right on the building. The grass outside was still in good shape.
[link|http://www.geoffmetcalf.com/pentagon/pentagon_20020316.html|http://www.geoffmetc...gon_20020316.html]
But agreed that Bin Laden is doing everything he can. However something as big as what he did on 9/11 can clearly be timed to a moderate extent. They timed the day to be one with symbolism for them. They could have trivially picked flights an hour later. The background research to have known that starting after trading hours would kill more people than starting before is not hard to do. Certainly it is easier than training pilots!
When they don't wait the extra hour, you have to wonder why not.
Cheers,
Ben