Any move to a global Test calendar and a new competition that brings together the hemispheres will not happen before 2024, says World Rugby.
Officials want one annual schedule for Tests to create a more meaningful and profitable competition format.
However, a proposal to get rid of July internationals and create an extended autumn window has been dismissed.
World Rugby says "strong progress" has been made on a parallel plan to refine the women's calendar.
Currently there are three Test windows when clubs are required to release players for international duty. However, the timing of those windows differs slightly between the hemispheres.
While northern hemisphere nations traditionally tour in the south in July and vice-versa in November, the Six Nations is played in February and March and the Rugby Championship takes place August to October.
Scotland head coach Gregor Townsend was one of those to support extending the autumn international fixture list - a measure that happened this year because of coronavirus disruption - at the expense of the July fixtures.
However, World Rugby has concluded that "retaining the existing July and November windows delivers the optimal environment for any new competition to be implemented from a player welfare, union and professional league financial, broadcasters and fans perspective".
Rugby Football Union chief executive Bill Sweeney, who is part of a six-person group working on the calendar, said in June that he had hoped a new global schedule could be launched for the 2020-21 season.