As noted in game, the release of the Plagueworks in Icecrown Citadel occurs 28 days after patch 3.3.0 was released. After the Plagueworks is available, you will then wait less than 28 days for the next wing to become active. The extended length of the initial 28 day delay is simply due to the timing of the Holidays.
In other news, the initial number of attempts to defeat the major bosses at the end of each wing of Icecrown Citadel has been increased by 5. This means you’ll have 10 attempts for Professor Putricide, 15 attempts when The Crimson Halls are available, then 20 when the Frostwing Halls becomes attackable.