Greenland has a single timezone for a 4-hour span. China has a single timezone for a 5-hour span. Having a single timezone for the contiguous US would definitely not be unheard of.
Guam is a bit of an odd duck because it is on the other side of the date line. The US currently spans from UTC-4 in Puerto Rico to UTC+10 in Guam - which is essentially the same as UTC-14. That's a 10-hour span, not a 20-hour one. Still, excluding the minor overseas colonial possessions would probably make the most sense.
Guam is a bit of an odd duck because it is on the other side of the date line. The US currently spans from UTC-4 in Puerto Rico to UTC+10 in Guam - which is essentially the same as UTC-14. That's a 10-hour span, not a 20-hour one. Still, excluding the minor overseas colonial possessions would probably make the most sense.