I visited the Royal Observatory’s Time Gallery in Greenwich a couple of weeks ago. The notion of publicly agreed shared time, based on Greenwich Mean Time, was something that emerged only in the 19th century, mostly to do with the arrival of the railways.
An interesting set of dates:
1853: A time ball drops on the roof at 1pm every day (other early systems include a cannon ball firing, a flag dropping, or a telegraph arm signalling)
1858: 98% of public clocks are set to GMT
1880: GMT becomes nation’s legal standard
1884: time zone system created, based on Greenwich
1924: the BBC introduces the ‘six pips’ as a public service
1927: a radio time signal is broadcast from Rugby Radio Station
UTC, or Co-ordinated Universal Time : 240 nuclear clocks, at 99 locations, are co-ordinated through BIPM in Paris; BIPM calculates a master time and sends it back again.