The official opening is June 1, 2010, as Peter correctly reported.
For sure, some people will get to play the entire 18 before then, but I think it will be limited to special groups [such as the Golf Club Atlas group that Ran is putting together for early May]. I don't think they will book tee times for the new 18 in April or May.
It's possible that some people will get to play the full 18 as early as October or November of this year, but I doubt they will cut cups on the newer holes until next spring, since the newer greens will not be up to speed with the older ones.