The Atlantic:

The time that ends up on your smartphone—and that synchronizes GPS, military operations, financial transactions, and internet communications—originates in a set of atomic clocks on the grounds of the U.S. Naval Observatory. Dr. Demetrios Matsakis, Chief Scientist for USNO’s Time Services, gives a video tour.

A little dry (and oddly shot/edited) but still an interesting overview of “the nation’s time keeping”.