Use the Auto-numbering nodes form to set the database to which auto-numbering should apply. You will select this database later on in the auto-numbering process.
Click the Fields button to specify, for each database, additional information about the codes to be numbered automatically.
Specify for how many days the codes (keys) are valid.
Example
Let's assume you want to create codes for the years 2014 to 2016, where the year is used as the prefix of the code, for example '15' for the year 2015. The codes are always valid for one year (365 days). As you want to create codes for a period of three years, enter 3*365=1095 or 1100 days (rounded up).