Devney mentions that she is focusing only on IANA timezones. See a list here https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

America/Detroit is a valid IANA timezone. Eastern is not.

Edit: Etzos has pointed out that US/Eastern is on the list. Thanks for correction.

Ah. I missed that while skimming through the page. I was primarily responding to the statement made that "they are also called “time zones” in casual conversation." They are time zones in the official sense of the word.

Speaking as if the Olson tz database is authoritative and official reminds me of when some small country cancelled summer time with only a few days notice and our OS vendors were not going to be putting out a patch in time. While explaining the process of downloading the Olson tz database and updating systems manually, a coworker asked who gave them (the country's government) permission to cancel DST. It took longer than it should have for me to come up with an explanation that sovereign countries don't need permission from the Internet or OS vendors to change their laws and regulations. The computers track the government actions, not the other way around.

  > some small country cancelled summer time with only a few days notice

Egypt just did that.

- In April, Egypt announced daylight time would start July 7. http://english.ahram.org.eg/NewsContent/1/0/204655/Egypt/0/D...

- On June 30, Egypt decided daylight time would start July 5. http://english.ahram.org.eg/NewsContent/1/64/232199/Egypt/Po...

- On July 4, Egypt decided not to have daylight time. http://english.ahram.org.eg/NewsContent/1/64/232478/Egypt/Po...

While you're right that countries don't need permission to change their timekeeping, they should be fully informed of the technical trouble they're creating when they make changes.

You'll notice that list includes US/Eastern which links to America/New_York as the correct "standard" for that timezone.

Edit: Just want to clarify that "Eastern" and others are indeed on that list and everywhere I've needed them have worked in place of the physical location equivalent. The physical locations, however, are the standard for the respective timezones--I am not commenting on the correctness of the GP post.

Thank you, I missed that. I have noted your correction in my comment.

If it helps, you can think of the IANA time zones as functions from UTC to local time. This is not quite the same as the political definition. For instance, both America/Boise and America/Phoenix are in the "Mountain time zone". But when viewed as functions, they're very different -- one is continuous and the other is not.

To add another layer of complexity, the tz database is capable of representing time zones whose definitions are themselves changing over time. If your state government decides to switch from Eastern to Central time next year, you still want to be able to accurately answer questions like "what was the current local time in this location at UTC instant t?".

Eastern Standard Time is an offset -5:00, not a time zone. Eastern Daylight Time is a different offset -4:00 that is used in many of the same time zones as EST, at different times of year.