Sometimes when I am editing I may accidentally edit the same page in different tabs, or I might forget whether I have updated the page earlier or not. I use a Save and Edit button when saving and when I save I want to know when I last saved based on the notice in at the top of the page, where I normally see a message like the following.
There is some sample code for a module that changes the message handling - https://atendesigngroup.com/blog/drupal-7-drupal-8-customize-or-remove-node-creation-message. How could I change it just to add a timestamp to the message?