Currently, Zammad will prevent you from editing or deleting your own internal notes after 10 minutes.
This apparently causes some frustration in our team because people want to use internal notes to track ongoing progress, for example, to have a note that is continuously updated to reflect the current state of an issue. The current behavior of Zammad unfortunately pretty much prevents this.
I do understand that this behavior is intentional for revision safety, but I think it would be useful to have this configurable (with a hidden option if need be). Then administrators could decide whether they prefer the revision safety for internal notes, or if the ability to track ongoing changes in a single note is more important.