The official Inauguration Day is January 20th. However, as that date falls on a Sunday in 2013, the public swearing-in ceremony will be held on Monday, January 21, 2013.
Yeah, like that really matters. Congress can meet on Christmas Eve to shove through bills that no one wants, Obama can sign legislation via autopen while playing in the waves in Hawaii, but a presidential inauguration on a Sunday? No way!
LOL!