The cooking time for boiling frozen sausage can vary depending on the type and size of the sausage. As a general guideline, it is recommended to boil frozen sausages for 15-20 minutes. However, it's important to ensure that the internal temperature of the sausage reaches 160°F (71°C) to ensure that it is fully cooked and safe to eat. You can use a meat thermometer to check the internal temperature of the sausage. It's also a good idea to follow the instructions on the package of the sausage, if available, as they may provide specific cooking times and temperatures.