Well, it's busy today. 20mins which means it's running full shows and if you get in line you're likely in the second show to load (or waiting for it to load.)
Pics on twitter show the line wrapping around the reflecting pool and toward MS.
On a related note, MS is only 15mins.
Since they're using the full gap-space between the building and the fountain to fill and hold people, the break between shows should be roughly the tip of the fountain. Ahead of the tip and you're in next show to load, past the tip you're in the one after that.