Enter the length of time that the license key string will be valid for. 

For example, you would enter [1]  and choose [month] to make the license key string valid for one month. Be warned that doing this means that at the end of the term the license key string will absolutely expire.

It is common to make the license key string &lt;b&gt;Never Expire&lt;/b&gt; instead. To do this leave the text box blank and choose &lt;b&gt;Never Expires&lt;/b&gt; from the select box.