Is an Associate Editorship in a good journal a very busy position? Should junior faculties at the very early stage (i.e. at the time of joining the department as a faculty) put an effort of being an associate editor in a high-impact journal? Or two or three years after working as a faculty, one should get into these editorial activities? To get tenure on the way down the road, how helpful this role is?
In my field, associate editors are not usually positions you apply for. Someone (usually someone else on the editorial board or from the journal staff) recommends you for the position on the basis of your reputation or previous work done with the journal, v.g. member of an advisory panel, long history of refereeing for the journal, i.e. you have to be a known entity.
Depending on the level of support, it can be quite time-consuming, especially if you want to do a good job, v.g consider going beyond the referees recommended by the system or by the authors, keep everything on track. I would ration myself only to so-many manuscript at once or else this would become all-consuming time wise.