"around 9am PST", which is 4pm GMT to us in Europe.
The four-player co-op treat is already out for PC and PS3 gamers. It adds two scenarios: Assault on Hab Center Andreas and Escape from Kalkys Facility. More DLC is planned.
More free and premium DLC is planned to be released say THQ and developer Relic. In the Exterminatus squad you can choose to be a Tactical Marine, Devastator or Assault Class.