Re: Prevent screen from powering off setting
As a rule, there is no such thing.
Go to Settings -> Display -> Sleep for options up to 30 minutes.
Depending on your phone and carrier, you may be able to access Developer Options - go to Settings -> About Phone -> and tap on Build Number several times until "You are now a developer" or some such appears. Now, Settings -> Developer Options -> Stay Awake ("Screen will never sleep while charging") but, as stated, that only works while the phone is plugged into a charger.