Other mistake: Near the end of the movie, after the cops storm the bank, all the cops walk into the vault, and as the camera follows them into the vault, you can hear the camera hit the metal vault door, and visibly see the camera shake from hitting it. (01:38:15)
Other mistake: When Washington went back to his room at the end just before he pulls the diamond out of his pocket. He unloads his Glock. The magazine doesn't have any bullets in it and there wasn't any noise of a bullet falling out of the chamber as he moves the slide back.
Other mistake: At 1:44:31 a close-up of a bank safe deposit records document shows box sizes that don't match the sizes of the boxes themselves shown at 0:58:41 and 1:55:21. The document shows box 378=3x10, 379=5x5, 384=5x5, 388=3x10, 396=5x5 but the boxes themselves appear to be 378=5x5, 379=5x5, 384=3x10, 388=3x10, 396=10x10. (01:44:30)
Answer: The aforementioned answer fails to keep in mind he is the owner of the bank and could've have done this hours before the bank was opened and or hours after the bank was opened. Dalton spent 3 days behind the wall. Mr Case had a special fixer, and she had the mayor in her pocket. It is a reasonable assumption that a billionaire like Aruthur Case would be able to have the contents of his safety deposit box removed with little to no problem. One way is "yes Mr. Mayor I will be giving you a blank check for your reelection campaign." The issue is this was a major plot hole that almost ruined a otherwise great and well thought out movie.