Ran into a concerning issue:
If you post a scheduled/delayed announcement with a file attachment, that attachment is immediately added to Files/unfiled section, where it can be viewed by anyone in the class.
This issue was escalated to us by an instructor who scheduled an announcement to post their midterm, and was unhappy to learn that the file was accessible to students before the time they had scheduled.
I imagine that the primary use of scheduled/delayed announcements is to support the dissemination of time-sensitive information (e.g. scheduling the release of assignment solutions after the assignment is due). For files attached to a scheduled announcement to not follow the same availability schedule as the content of the announcement strikes me as unintuitive.
Here's a screenshot of a scheduled announcement:
The content of the announcement may not be visible, but the attached file will be...
Wanted to give a heads up in case this is useful to anyone else.