When I read the December 2012 FIFA ranking release, I thought there was a little mistake:
"The next FIFA/Coca-Cola World Ranking will be published on 17 January 2013."
17 January is Thursday, not Wednesday.
However, FIFA have published all the 2013 release dates and it seems they have moved the release date from Wednesday to Thursday.
Most likely, as Tobcoach said, they made this move in order to include the Sunday matches in every ranking.