By one second. On December 31, 2016, at 11:59:59pm UTC, one second was added to Universal Time Coordinated (UTC), which is the basis for the worldwide system of timekeeping.
By one second. On December 31, 2016, at 11:59:59pm UTC, one second was added to Universal Time Coordinated (UTC), which is the basis for the worldwide system of timekeeping.