The 24 > 12 hour time shifting problem has happened off and on to my 5.2 and 5.3 over the last couple of years, both with Tiger and Leopard. Seems to be random, and my fix is to quit NUD, reselect 24 hour time format in System Preferences (International - same as it was before), and relaunch NUD. Usually works - if not, I just do it again, and wait for the next hiccup, which usually occurs once every two months or so.
Fred