Never change their clocks. Always on GMT-6.
Belize (CST) 
Canada (CST) Regina
Costa Rica (CST) 
Ecuador Galapagos
El Salvador (CST) 
Guatemala (CST) 
Honduras (CST) 
Mexico (CST) Chihuahua, Mexico City
Nicaragua (CST) Use GMT-6 only during their Standard Time period.
Mexico Ojinaga
United States (CST) Chicago, Indiana — Knox, North Dakota — New SalemOn Daylight Saving Time they switch to GMT-5 (CDT).
Use GMT-6 only during their Daylight Saving Time period.
Canada (MDT) EdmontonOutside DST they sit on GMT-7 (MST).
GMT-6 is 6 hours behind Greenwich Mean Time
The GMT/UTC minus 6 hours offset is used in the Central Standard Time Zone in USA. It is also in use when USA states in the Mountain Time Zone operate Daylight Saving Time.
Enter your location or any place of your choice for more comparisons.
Nowadays, Greenwich Mean Time, abbreviated as GMT, is a time zone designation rather than a time standard. Time difference between time zones can be expressed by the GMT or UTC hour difference.
@time_gadgets