Time has come today.........

In 1675 the Royal Observatory at Greenwich established GMT [Greenwich Mean Time] and the system of Longitude to aid mariners. This system divided the world into 360 degrees with 15 degrees equal to one hour of time.

The issue was less a concern about time, [all time was called "local time" and kept by a town clock], but more about location of ships at sea. A prize was awarded for the solution to finding accurate longitude within 30 nautical miles. This was the Longitude Prize of 20,000 pounds [about 6 million Euros today]. The prize was won in 1827 by John Harrison with the invention of Marine Chronometer, the first accurate marine clock. Setting the clock to GMT on board ship allowed the Captain to know how far east or west of London he was compared to local time at noon, solar mid day. If the local time was Noon but it was 3 PM in London then he was 45 degrees longitude west of London. The Earth is divided into 24, 15 degree zones.

By 1847 British Railway had adopted GMT as "Railway Time" to maintain the schedule for trains. In 1880 it became Britain's legal time. Time keeping on American railroads was much different with each railroad keeping their own time based on their headquarters. Large railroad stations had multiple clocks for each railroad. In 1863, Charles Dowd purposed a system of one hour Time Zones the first centered in Washington 75 degrees west of Greenwich.
The railroads adopted a similar system with local resistance until 1918 with the Standard Time Act.

However, Sanford Fleming proposed a single world time zone with a 24 hour clock in 1876. Such a "universal day" was widely discussed and in 1884 The International Meridian Conference agreed to the use of the 24 hour clock beginning at Greenwich at midnight but also agreed .."shall not interfere with the use of local or stand time where desirable"

In effect we are using GMT, now called UTC [Coordinated Universal Time], today and converting to local time to accommodate custom. As we become more global and through use of the internet, the use of UTC will increase until we all accept Universal Time as the standard. The US Military has switched to Zula Time, UTC, as their global standard.