[12/21/12 Just in: Christmas Eve 2012 is a day off. The White House issued a Executive Order. https://alexwdc.wordpress.com/2012/12/21/federal-employees-president-barack-obama-grants-leave-on-christmas-eve/]
In an update to my post from last year, I don’t think that there will be an Executive Order for an early dismissal. This prediction is especially true since the Congress and the President are engaged in high-stakes negotiations.
Nevertheless, it seems to be more likely these decisions will be made at the agency level.