You may optionally specify a time period at which the litter will automatically become invalid (you should not fill in the completion date at all for this method). A drop down box allows you to select from Never to 6 months. If you use this method, the litter will automatically complete after the specified amount of time. Again, this method is inaccurate, although easy as you can guess the age of the litter (if it was brought in), and simply say ``assume all the animals in this litter will be adopted after 6 months old''.