Now backup of one course is ENTIRELY encapsulated inside backup_scheduled.php.
And a backup of EVERY course can be executed invoking try.php.
Backing up to a custom directory is working too !!
They are preliminary versions, of course, but seem to work fine :-)
Now I'm going to make all the necessay structures to support the cron system
and to be able to inform the admin about every scheduled backup process.
Ciao :-)