>This package was installed on 3/31. Why are they building a queen cell?
Packages often supersede just because they are stressed from shipment. They also supersede because they think the queen is failing (everything get's blamed on the queen though including shipping), either because of her laying, her pheromone production etc. Or, in recent times, a lot of queens get superseded because they are not fertile enough because of Apistan and Checkmite buildup in the hives.