What was the first country to adopt time zones? When was this?

Timezones were really not needed much until the railway became a major form of transportation. Most places based their time on when the sun would be at its zenith which created problems when traveling either east or west on a fast train. On 2 November 1868 New Zealand became the first country to adopt a standard time which they designated as New Zealand Mean time. It was 17 and 1/2 hours ahead of London time. Within 35 years most places in the world had adopted a standard time, however, not all adopted them in hour increments and some still have half-hour differences between their neighbor. Some timezones end up quite large like China, while others have almost no one living within the zone.

https://en.wikipedia.org/wiki/Time_zone