How did the person who set the time on the very first clock know what time it was?
It all started with the railroad actually. At first all the towns would have their own time, which corresponded with where the sun was during the day. But then, when the railroad was built for trading and passenger transport, all of the town's had to have the right time in order to catch the train so everyone would link their clocks with the railroad time. There were actually "time wars" where towns would protest in favour of having their own time, because they had become personally attached to their autonomy of time. Trrue story.