It doesn't really work that way.
Also, the print speeds given are going to be under ideal conditions.
These are very large high-res images that are ripped to the printer. Ripping a large file takes time above and beyond the print time.
That said, the banner is displayed near where it was printed so that saves time. The graphics layout can be done quickly but still takes time. But from what I understand there was a laspe of hours between the actual bombing and when the rescuers (and media attention) arrived on the scene. In fact on Fox there was some discussion of the big delay in the rescue efforts.