By default, nations in the lists are sorted by time of last login, and nations with more recent last logins are at the top. The results and sorting are updated once per day, approximately two hours after the end of NationStates' major update (you can see below when results were last updated). Once you have generated the lists and endorsed everyone, there is no point regenerating them for the same nation until after the following update. If you do regenerate the lists within the same day (e.g., if you did not have time to endorse everyone), the sorting will be the same, so you can pick up endotarting at the nation you stopped earlier.
Last update: Fri Apr 3 01:12:06 EDT 2020.