I have it set to a minute. But sometimes my phone will lovk before that. And i will unlock it and it will lock again.! It annoys the heck out of me! Is there a way to fix this? This is my second Driod 4!
I had issue with my Eris fade time going back to ten seconds,so that it goes dark and locks,even though I set the timer for thirty seconds through some option toggle app. Idk if this is your issue,or if it closely relates but if I go into options and set the fade to 2 mins it stays UNTIL I restart the phone than it goes back to a default ten second. Can only say how my old phone works but try that manual option trick and see if it resets after rebooting.
Sorry is this answer is no help or not quite to the specifics you want but I share your frustrations.
If if doesn't have a hole for the proximity sensor it could be causing that problem. Other than that, it's all personal preference. I use screen protectors because I don't like the look/feel of them, and I've never had issues with screens getting scratched.