The thinking is that Disney is aiming for April 22, which is both Earth Day and the anniversary of the Animal Kingdom. However, at this point no one really knows. Since you are going in March you will likely have the chance to ride what Disney calls the "soft opening" of the ride. This happened to us with Mission: Space a few years ago. We were there a couple of months before the official opening but I read here that Disney was doing the soft openings during the evenings. Sure enough, it was closed during the day but every evening we were there they moved back the barriers and let people on. We rode every night of our stay. Keep reading the boards and hopefully you will be able to ride Everest when you go.