You can bypass that limit by creating as many cron tasks (using FTP or Local HDD to store backups) as needed.
To store 7 days backups -> create 7 different tasks with different FTP or local paths (e.x. /user_backups/0 - for Sunday, /user_backups/1 - for Monday, etc).
For IP/Username/Password (FTP) use your reseller's credentials.
cd /home/admin/admin_backups/
mkdir /home/admin/admin_backups_$(date +\%d_\%m_\%Y)
mv /home/admin/admin_backups/* /home/admin/admin_backups_$(date +\%d_\%m_\%Y)
honestly i dont know if there is a backup_post.sh script from directadmin templates for run this commands just after backup complete, i use to do that the day after with crontab