Every drone on the Emperor was working by the end of the first day, along with the Emperor’s engineers. They had many more ponies than that who could’ve moved shovels and turned dirt, but that wasn’t what they really needed. They only had the one digger, made from a repurposed APC. Since most of their construction was underground, there wasn’t really anything the soldiers could do that Forerunner’s drones or Motherlode’s population couldn’t do better.