There is no "official" Scheduler for automatic export from the firewalls - yet. But you can ask your account's SE to sign the Feature Request for you.
Anyway there are some ways to trigger config Backups from external Server
1. Use the XML API How to use the XML API to backup your firewall configuration
2. Or use remote ssh login (with public/private key for passwordless login) in a shell script on an external Server and execute backup commands:
scp export configuration to USER@SCPHOST:PATH
tftp export configuration to TFTPHOST
If Panorama is used, then you do have the full ability of scheduling config-backup exports: