As was announced by IERS (International Earth Rotating and Reference Systems Service) in Paris, a leap second will be inserted at the end of December 31, 2016 at 23:59:60 UTC (Coordinated Universal Time) to synchronize atomic clocks with astronomical time.
The sequence of dates of the UTC markers will be as below;
e.g.) Japan
After this leap second change, ensure the adjustment in time either by manual time adjustment or automatic time adjustment if your watch has radio wave controlled function or receiving GPS signals.
This will ensure the time is set correctly for Radio Wave or GPS watches.
Radio Wave controlled watch >> manual time adjustment
GPS solar watch >> http://www.seikowatches.com/information/popup_2016_02.html
About Leap Second
The leap second is to compensate for deviations from the "Universal Time" (UT) which is astronomically determined and the "International Atomic Time" (TAI). 1 second may be added (deleted) once a year or every few years at the end of June or December.
(December, 2016)