To schedule a post to update at a certain time, select that time within the “republish date” window. If the date is in the future, the “Republish” button will change to “Schedule republish”.
Republish allows users to make and save edits to an existing post without publishing, then save changes as a new draft and schedule changes for publication at a later date. After publication the new draft and the original post will merge to create a single record; the original URL for the existing post will be preserved unless intentional changes are made.
In order to trigger a timestamp change upon publication, check the box in the Story Timestamp field. This will update the timestamp on the reader frontend, while preserving the original publish date in the edit post screen.