I can believe that, though I've only been at the site once as a kid when visiting Dallas.
However: Have you ever performed a critical task, missed your chance at the easy way, and had to do it the hard way?
Maybe Oswald almost chickened out, was nervous, wiped the sweat off his lip, triple checked his rifle, who knows what.
He was about to assassinate the President of the United States, for gosh sakes. I can't even imagine the pressure, and certainly don't like to think about what was running through Oswald's head when he allegedly did it.