For some evidence of this, consider that sundials have existed since about 1500 BCE. The existence of such a device easily disproves the notion that the "curre

For some evidence of this, consider that sundials have existed since about 1500 BCE. The existence of such a device easily disproves the notion that the "current time" was ever the same globally. Even mechanical clocks would obviously need to be set such that they would agree with a sundial, or the reading of the mechanical clock would be useless in a world where others are using sundials.