Timezones; sure. But what about before timezones got into use? Or even halfway through - which timezone, considering Königsberg used CET when it was part of Germany, but switched to EET after it became Russian. There's even countries that have timezones differenting by 15 minutes.
And dont get me started on daylight savings time. There's been at least one instance where DST was - and was not - in use in Lebanon - at the same time! Good luck booking an appointment...
Not to mention the transition from Julian calendar to Gregorian, which took place over many, many years - different by different countries - as defined by the country borders at that time...
We've even had countries that forgot to insert a leap day in certain years, causing March 1 to occur on different days altogether for a couple of years.
Time is a mess. Is, and aways have been, and always will be.