I have this issue with the S4, please allow me to elaborate. The biggest annoyance I have with this is not being able to use an alarm clock. When my phone is in "sleep" (black screen), I'm pretty sure the time doesn't change. Since the time doesn't change, my alarm clock wont go off at the time its supposed to since it doesn't know what the current time. It's only when I tap a button (home-screen-button or power button) that awakens the screen will I see the time refresh (maybe a 1 sec lag from old time to current time). I just got the phone, upgraded from the S3 which didn't have this issue. I would prefer not to hard reset/format the phone if anyone has any luck with any clock apps mentioned here or if this is an OS issue which might cause any app to not keep time the way it should. Thanks.