Set an expiry date for your posts with these simple steps:
  ① Click Post > Add New or Event > Add New (you may also open from existing posts)

  ② Scroll down and on the right side, find a widget named Publish 

  ③ ☑ Datetime of Expire 
Inside the Publish, you will see an option called Datetime of expire. Tick it and a rectangular bar will appear.

  ④ Click the rectangular bar to select date and time, then click Done.

NOTE: Remember to hit the Publish button after editing the entire post or event!