It was stated by Disney staff previously that the Fastpass would become available when the ride opening is announced, which will not be prior to the 'media preview' 30th Apr - 2nd May.
It seems likely that they would want the ride complete and fully functioning for the preview/dedication three days and it does look like they are making final touches at the moment.
Would seem strange to me to make such a large display of having the preview and then not opening the ride to the public on Saturday 4th. Hopefully the media will get some insider reports as of Wednesday.