The names of time zones should be treated as proper nouns. A time zone is a geographical area. Do not specify standard time and daylight time, which refer to clock settings within a time zone at specific times of the year, unless you are referring to an event, such as a webcast, where this information is important.

Microsoft style

Central Time

Eastern Time

Coordinated Universal Time

Pacific Time

Not Microsoft style

Central Daylight Time

eastern time

eastern standard time

Pacific time

It you are referring to a time zone as a geographical area, as opposed to indicating a time within that area, make explicit reference to the time zone as such.

Microsoft style

The event begins at 21:00 Eastern Time. Broadcast times may be different in the Pacific Time zone.

Do not use Greenwich Mean Time or GMT by itself unless you have no other choice. The current internationally accepted name for Greenwich Mean Time is Coordinated Universal Time. Because not everyone may be familiar with this name, it is all right on first mention to refer to Coordinated Universal Time (Greenwich Mean Time). If you must abbreviate Coordinated Universal Time, do not use CUT. By international agreement, the universal abbreviation is UTC. Do not refer to Coordinated Universal Time as Universal Time Coordinate or Universal Time Coordinated.

Do not abbreviate the names of time zones, such as PT, ET, and UTC, unless space is severely limited.

If you do not define a context, some time zone names can be ambiguous. For example, North America and Australia both have an Eastern Time zone. Unless you are creating a generic example where geographic location is not important, be sure to resolve such ambiguities. The simplest way to do so is to denote an offset from Coordinated Universal Time that uses standard (not daylight) time. In this case, it is all right to use the abbreviation UTC, as in the following examples:

Not all time zones have names. For time zones without names, refer to the offset from Coordinated Universal Time, as follows:

UTC+7

See also A.M., P.M.