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The concept of standard time zones had actually been suggested by several professors going back to the early 1870s. At first, it was suggested that there be two time zones, set to when noon occurred in Washington, D.C. and New Orleans. But that would create potential problems for people living in the West, so the idea eventually evolved into four "time belts" set to straddle the 75th, 90th, 105th, and 115th meridians.

On October 11, 1883, the General Railroad Time Convention met again in Chicago. And it was formally decided that the new standard of time would take effect a little more than a month later, on Sunday, November 18, 1883.


www.thoughtco.com/why-we-have-time-zones-1773953