Each content app has a preset Time to show value.  This value defines how long each content post is shown at it's turn on the show cycle. 
Note! Videos make an exception. They are always shown to the full length. 


E.g. A post coming from My Content for DEMO's app will be seen on the screen for 8 seconds if the post uses default Time to show value. 

You can change the Time to show value from the APPs tab. And you with manual content posts, made with My Content, you can change the value when posting your message. Find out more about publishing manual posts.