If you choose to use an excluder, similar to keeping the queen in a clip, do not leave the excluder on more than 3-4 days--it's used simply to keep them from absconding, ensuring they establish themselves in your hive. If it's a virgin queen (e.g. secondary swarm), the excluder will prohibit her from going on mating flights and if left on the hive (either intentionally or forgotten) too long, she'll miss her mating window and be a drone layer.