Good morning to you! Hearing that your Samsung S7 switched to Central Time Zone, which resulted in you oversleeping is a very urgent matter. I personally apologize for the inconvenience. I also see you've been provided potential answers to this issue by our Community members (e.g. checking to make sure that the automatic date and time setting is turned on and checking to see if your device is set on Network time). Both are very good troubleshooting steps to consider.
I also further investigated this matter. I can assure you that this is not a known issue with your device. Just to be sure, this website link will assist you with checking your device's Data and Time settings at: http://vz.to/2vQx7tU.
This website link will provide you with assistance to automatically populate the date and time based on your location at: http://vz.to/2vPYAvX. I hope this is beneficial.
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