There is a very small (but not zero) chance that one of the files in the backup set might be backed up as an update is being performed on a related file. In 30+ years of working with this data, and thousands of backups, I've never seen it happen.
But programmers are a cautious lot so the warning exists. Personally, I'd never bother kicking people out of Adagio just to do a "middle of the day" backup.
If there's a crisis that necessitates going back to the backup, your Adagio Consultant would easily be able to get you back up and running from the backup you had made.
Adagio 9.3A Versions have the ability to automatically make a backup before every critical function. This process does not wait for everyone to exit the system. We felt that would be too disruptive.
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Andrew Bates