Gaining and losing an hour is a yearly thing.
Gaining a day happens once every four years.
But gaining a second?
It actually happens about every 18 months [1] (but not on any type of set schedule). Wall Street is freaking out [2] about it. What about you? Will you be watching Bobby Cannavale screaming “Leap Second!” [3]? Or will you just spend an extra second sleeping tonight?
[1] https://en.wikipedia.org/wiki/Leap_second#Insertion_of_leap_seconds
[2] http://www.wsj.com/articles/markets-are-jumpy-over-coming-leap-second-1431988248