They expected to be up by 2:00pm pacific. It's currently 1:50pm pacific
Posted by Bashiok on April 30th.
We'll be bringing down the Diablo II realms at 10:30 a.m. PDT, May 2 to begin the ladder reset. We estimate the maintenance could take up to four hours to complete, and expect the realms to be available again by 2:00 p.m. PDT.
For more information on the ladder reset please read the original announcement here