Check these out while you're waiting:

FAQ section on clocks

Time keeping in Ancient Rome by /u/Celebreth

When was our concept of time developed? How did other cultures in the past measure time? When did the world agree to the 24 hour day? by /u/Gargatua13013 and /u/yodatsracist

How did Native Americans measure time and distance? by /u/Muskwatch

This may be silly but how did the whole of humanity standardize on one set of measurements of time (less than a day)? by /u/vmos

How Did Medieval Monks Keep Time?