When the backup retention changes to a non-zero value, the first backup occurs immediately. Changing the backup retention period to 0 turns off automatic backups for the DB instance, and deletes all existing automated backups for the instance.
Unfortunately one of the major backup related pain points with RDS currently is you have no way to interact with the automated backups aside from restoring an instance to a point in time. They are also deleted when the instance is deleted. Manual snapshots aren't. Manual snapshots can be used to launch and new instance, or they can be moved to a different region. You MUST do your own backups of the databases if you want to get them "offsite" or off account. Like I said, PITA right now and from what I here a common request on RDS is being able to get at the automated backups and snapshots so you can move them offsite.
When the backup retention changes to a non-zero value, the first backup occurs immediately. Changing the backup retention period to 0 turns off automatic backups for the DB instance, and deletes all existing automated backups for the instance.
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overvi...