Ducklings are okay to sleep outside, depending on the weather. So long as you have a safe, predator-free environment for them to rest. If you have a safe house or pen outdoors, and the weather is agreeable, you can transfer your ducklings outside between three and five weeks. However, until the ducklings are seven to nine weeks old, they have trouble regulating their temperature, especially if they are outside. So we recommend you use a thermometer to monitor the temperatures.