When were time zones established?

Time zones were established in the United States on November 18, 1883. The motivation for standard time came from interstate trains, which had to coordinate when they would arrive and depart.

Regional time zones for the US & Canada were used in the late 1800s for trains as sferik pointed out.

Their use universally began thanks to ‘ol Sandford Fleming who was a well respected engineer of the time. Like all good ideas, it wasn’t fully accepted when he proposed it and wasn’t implemented globally until 1929.

See the Wikipedia article – interesting stuff really.

calculated off greenwich mean time (in the UK)

GMT – Greenwich Mean Time
Time zone offset: UTC
GMT is in the same time zone as Coordinated Universal Time (UTC)
Note that some places observe daylight saving time/summer time during summer, and are therefore using BST (United Kingdom) or IST (Ireland) instead in the summer. See below for details.

Time zone abbreviations: GMT, UTC
Full name is Greenwich Mean Time
UTC – Coordinated Universal Time (Alternative)

via http://www.timeanddate.com/library/abbreviations/timezones/eu/gmt.html

Greenwich mean time was based upon the time at the zero degree meridian that crossed through Greenwich, England. GMT became a world time and date standard because it was used by Britain’s Royal Navy and merchant fleet during the nineteenth century. Today, UTC uses precise atomic clocks, shortwave time signals, and satellites to ensure that UTC remains a reliable, accurate standard for scientific and navigational purposes. Despite the improvements in accuracy, however, the same principles used in GMT have been carried over into UTC.

UTC uses a 24-hour system of time notation. “1:00 a.m.” in UTC is expressed as 0100, pronounced “zero one hundred.” Fifteen minutes after 0100 is expressed as 0115; thirty-eight minutes after 0100 is 0138 (usually pronounced “zero one thirty-eight”). The time one minute after 0159 is 0200. The time one minute after 1259 is 1300 (pronounced “thirteen hundred”). This continues until 2359. One minute later is 0000 (“zero hundred”), and the start of a new UTC day.

To convert UTC to local time, you have to add or subtract hours from it. For persons west of the zero meridian to the international date line (which includes all of North America), hours are subtracted from UTC to convert to local time. Below is a table showing the number of hours to subtract from local time zones in North America in order to convert UTC to local time:

via http://www.dxing.com/utcgmt.htm

Greenwich Mean Time (GMT) is also known as Zulu Time and UTC (Universal Time Coordinated). The standard by which all World Time is set was agreed at the 1884 International Meridian Conference at Washington DC, USA placed Greenwich on the Prime Meridian (Zero Longitude).

So…you might as why does the Prime Meridian (Zero Longitude) pass through Greenwich? See below…

The International Meridian Conference
Washington DC, USA – October 1884
It dates back to October 1884. At the behest of the President of the United States of America 41 delegates from 25 nations met in Washington, DC, USA for the International Meridian Conference.

At the Conference the following important principles were established:

1 – It was desirable to adopt a single world meridian to replace the numerous one’s already in existence.
2 – The Meridian passing through the principal Transit Instrument at the Observatory at Greenwich was to be the ‘initial meridian’.
3 – That all longitude would be calculated both east and west from this meridian up to 180.
4 – All countries would adopt a universal day.
5 – The universal day would be a Mean Solar Day, beginning at the Mean Midnight at Greenwich and counted on a 24 hour clock.
6 – That nautical and astronomical days everywhere would begin at mean midnight.
7 – All technical studies to regulate and extend the application of the decimal system to the division of time and space would be supported.

via http://www.timezone.com/library/itsabouttime/itsabout0009

here are some cool time zone links

http://www.timeanddate.com/worldclock/
http://www.timezoneconverter.com/
http://www.worldtimeserver.com/
http://wwp.greenwichmeantime.com/time-zone/