It's really just a sneak peak. They were actually telling everyone to not use the words "opening" or "preview" because right now it's just so that the CM's at Soarin' can practice loading and unloading real people.
Your best bet is mid-day, between 1-7...but there really isnt a way to tell if it's going to run until you get there. Even some of the people who work at Soarin' don't know if guests will be riding until they get there.