You can leave it in overnight. just place it about 2-3 inches in front of their hide and make the room dark. My bp occassionally won't eat at feeding time, but will eat sometime during the night. Just make sure that you dispose of the prey if it is still there the next morning. If you don't see it the next morning, make sure you check around the enclosure to make sure it didn't get dragged into a hide or covered with substrate, or you will smell it later.