RDS data consistency across accounts and Min AWS Backup frequency

Hello.

I think it is possible to easily replicate RDS PostgreSQL across accounts using AWS DMS.
https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Source.PostgreSQL.html

I think the minimum backup frequency for AWS Backup can be set to one hour.
https://docs.aws.amazon.com/aws-backup/latest/devguide/plan-options-and-configuration.html

The backup frequency determines how often AWS Backup creates a snapshot backup. Using the console, you can choose a frequency of every hour, 12 hours, daily, weekly, or monthly. You can also create a cron expression that creates snapshot backups as frequently as hourly. Using the AWS Backup CLI, you can schedule snapshot backups as frequently as hourly.

There is no way to achieve synchronous replication between two accounts, but you can setup your own replication with pg_active to setup a self managed asynchronous replication.

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.PostgreSQL.CommonDBATasks.pgactive.html