Here's a fantastic link that explains our relationship to time measurement very well...
A Few facts about GMT & UTC
A very good read and takes some of the natural xenophobia out of a French title -
Universel Temps Coordinné
I think anyone who has anything to do with navigation, pilots of land, sea or air, should make a regular pilgrimage to Greenwich to the observatory to see how our understanding of time has evolved. If you're British, than you can take special pride in how we gave the world the essential knowledge to be able to get about on our planet.
Cheers,
TheOddOne