Do you have your device set to automatic date and time when you are experiencing these symptoms?
Just to clarify, if you input the time manually the time still changes back to Eastern Standard time?
Do you experience these symptoms if you test your device in safe mode? If your phone is misbehaving, it's possible that a third-party app is causing the issue. To figure out what app is acting funny, you can use the Safe Mode feature. In Safe Mode, your phone won't run any third-party apps. This allows you to easily identity and remove the app that may be causing the problem. Give this link a try: https://www.samsung.com/us/support/answer/ANS00062983/
I would also recommend trying to wipe the cache partition on your device. The system cache partition stores temporary system data. It's supposed to allow the system to access apps more quickly and efficiently, but sometimes things get cluttered and outdated, so a periodic cache clearing can help make the system run more smoothly. Give these steps a try:
This is happening to me too (and many others based on other threads on this site). You can tuen off automatic time, but it turns back on a few days later and problem returns.