The residence time is the minimum length of time that data must spend in the database before it meets the archivability criteria. Residence times can be set in application-specific Customizing.
The retention period is the entire time that data spends in the database before it is archived. The retention period cannot be set.
If the residence time is a month, data that has been in the system for two months will be archived. Data that is only three weeks old remains in the database.