[Zubersoft]

The code for keeping the screen on has not changed for a long time. You can try going to Settings->Display Settings and enable "Hide the navigation bar" which will enable immersive mode on older devices. That may keep the screen on even if the current method doesn't work on your device. 

One thing I should mention is there is a 1-hour time limit where, if the screen has been kept on and there has been no interaction of any kind with the device for over an hour, the screen will be allowed to turn off. This is to prevent the battery from being completely drained if the user happened to leave their device on accidentally.

Mike