In reality the attraction will open probably in April, first for CM previews, AP previews then guest previews. The official opening however is in May. Another factor possibly to take into account is that Soarin' is opening on the same day.... maybe this is further behind schedule than Motors, Action. Also, these attractions are 50th Anniversary “gifts” for the Disneyland 50th Celebration which kicks off May 5th.
Also whilst the show building may in fact be complete, the CMs will be in rehearsals for a long time, as it will all have to be very tightly choreographed.