iPhone 5 time off by one hour.

I just purchased a new Sprint iPhone 5 last week. This morning I woke up and the clock was off by exactly one hour. I tried turning the phone on and off and resetting it to no avail. Finally I went into settings > date & time and turned on and off the automatic time function and it fixed the problem for about 4 hours; however, just now it reverted to being incorrect. Anyone have any ideas as to what might be going on? I'm running IOS 6.1.3 which I believe is the most current version.

Thanks!