How to configure multiple scheduled backups in Plesk?
For example, create weekly backups on Wednesdays and Saturdays.
This feature is yet to be implemented in Plesk. Vote for including it in future releases on our UserVoice portal: Multiple backup rules or more options.
Top-ranked suggestions are considered to be included in future Plesk versions.
As an alternative, a scheduled task using the utility pleskbackup can be created: Reference for Command-Line Utilities, Plesk for Linux pleskbackup: Backing Up Content and Configuration.