Screen burn depends on 2 things - how bright the screen is turned up and how long the same thing is on. If someone leaves the home page on almost all day, and it's at 100% brightness, any LCD screen will eventually burn in. If you reduce the brightness to something comfortable (I find 20%-25% about right in a normal room or office), and you keep the screen blank unless you're using the phone (30 second timeout or
Proximity Service running and you put the phone down face down, it should take years to get burn-in. (My over-5-year-old Note 3 has no burn-in.)