Man DRK's got an awesome CD.

Warrior: 6 seconds can't fall below 1 hp. Shortest CD.
Dark Knight: 10 second buff that activates ANOTHER 10 second buff upon hitting 0 HP. So you get the same kinda invuln a WAR gets for 4 extra seconds. The trade off is you need to be healed during it.
Paladin: 10 seconds no damage. Longest CD.

Now, correct me if I'm wrong please but DRK's living dead wears off after 10 seconds (death) or once they've been healed for 100% of their HP (but they don't have to be healed TO full)