From Frelorn on the OFFICIAL LOTRO FORUMS:
We had originally scheduled Update 18 to go live on this upcoming Monday April 11th. After finding a few things we wanted to tweak as the team was doing the final QA pass, we are delaying the update by one day. Update 18 will be going live on Tuesday April 12th. We feel the is was the best course of action and allows us to put out a better update. Thanks for your understanding, and we will see you all in-game.