Under settings> time & language> date & time, do you have it set to "set date and time automatically" ON & "set time zone automatically" ON, right? If that still doesn't help, try resetting your phone and see if it hosts the correct time.
You might have to adjust the time manually. That's really odd. A few months ago, I went to Panama City Beach and both my 640 XL & 635 automatically adjusted the time within minutes of crossing the county line from Gadsden County to Jackson County crossing the Apalachicola River on Interstate 10. My 635 is running Windows 10 while my 640 XL is still on WP8.1.