Until the eggs hatch. Or, if you don't let them sit, it might last on it's own for a few weeks. You can tell if it's nesting bomb because it's a huge green mess, often at high velocity. If it's a normal sized poo or yellow then there might be something else. If it's just a big green...
If it's the hens, and you say that they just finished laying? That's the nesting Muscovy duck bomb. It should be a foul large green mess that they make once or twice a day, or that they aim at people who try to pick them up. The Nesting Bomb is a normal part of Muscovy life.