According to the cplusplus.com,
A range of
61 allows for up to 2 consecutive leap seconds on December 31st of a given year, probably mistakenly because in years that require 2 leap seconds, these are not added on the same day.
Newer versions of the C Standard correctly assume that at most one leap second will be inserted at a time on any given day.
As explained in detail in https://en.wikipedia.org/wiki/Leap_second leap seconds are inserted in December and/or June in order to avoid a drift longer than 0.9 second, hence the maximum value for
tm_sec should be
60 instead of