Why Do Days Start At 12 O'Clock?

How was time created? How did one minute become 60 seconds and one hour became 60 minutes? Why is time segmented into 12-hour periods? How do clocks work? Why is a year 365 days? Why is there an extra day in February every four years? Does time have a beginning or an end? Is time travel possible? Answers to all of your time questions with Andrew Novick of NIST, the National Institute of Standards and Technology.