The International Earth Rotation and Reference Systems Service can insert or remove leap seconds from the last day of any month ( June and December are preferred ).

The International Earth Rotation and Reference Systems Service ( IERS ), formerly the International Earth Rotation Service, is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter ( EOP ) and International Celestial Reference System ( ICRS ) groups.

The International Earth Rotation and Reference Systems Service ( IERS ) specifies both years to 12 significant digits by referring to an article which specifies both in terms of a Julian millennium of 1000 Julian years.

0.005 seconds.