on the same page where you want to show your show message widget place a microflow timer widget (Available on marketplace) inside any data container
in microflow timer widget select a nanoflow (newly created) in second picture and configure settings
now go to js action and open it and click on code tab
write a code in like picture below [target show message activity close button by its class and just click]
Note: microflow timer widget interval(in behaviour tab) will be time of hide the show message activity
I hope it will help you
You can display the message in a popup page and make a microflow thats triggered when you open the page that closes said page after x seconds, using the delay activity java action in a microflow or the .Microflow Timer on your page.