Along with ts678, you could backup every day or hourly. If there are files you don’t want backed up that might be in the folders to be backed up then you can ignore a designated folder and drag and drop files not to be backed up to it.
Duplicati won’t re-backup the same files unless they change in some way because there’s no need to. It would be a complete waste to do so 
The biggest thing is to simply be sure Duplicati is running the backups.