Up until a few days ago, the people who were supposed to come to work at midnight to shut down the system were expecting to be told that they are not essential, so don't show up.  Maybe they were already told, and then no one told them the government was back on. 

More likely, the people who write the press releases figured they should add an hour and minute, and maybe that's the way it was last year, so why bother to ask if anything had changed?  Or the people that plan the outage, decided it wouldn't really matter if they did it at 5pm instead of midnight, and they didn't even know about the press release that said otherwise. 

IRS is a big place.  Don't ever expect coordination from the many arms of the octopus.  (Or are they legs?)