Then that wouldn't make sense for the chain game aspect of this quiz. Maybe just a little rewording of the clue to include "previous clock country" or something along those lines.
According to the official website of the Swiss watch industry "The Swiss watch and clock industry appeared in Geneva in the middle of the 16th century." 600 years before that is the middle of the 10th century. The Serbian claim seems to be based on Lazar the Serb "who invented and built the first known mechanical public clock in Russia in 1404". (Wikipedia) Did Serbia also invent a new way of reading the calendar?
Sorry, i had bad sources. I'm gonna fix that.