Hi!
Yes - it is awful with "line zero" : There were hard scientific battles if London or Paris will be the "line zero". There were times, when both lines in their sovereign territory were used. Britania then ruled the waves and had won: Greenwich was now "line zero".
And the second awful thing : The planets and the moons don't behave metric. The bloody earth needs 365.2524 day to surround the sun. And the naughty moon does not have a clear relationship to the sun. The only thing already the old greek knew was that the moon is every 18 years nearly at the same position: The great (moon) year.
And the only (?) try to get a metric time was the french revolution. But the metric time never succeeded. The idea was: The day with 10 hours, the hour with 100 minutes, the minute with 100 seconds. This revolution time was never used. In opposite to the metric french revolution calendar, which had a livetime from 1792 to 1805.
Winni