The main part of each conference will take place after sponsor expos and tutorials; usually Tuesday through Thursday. The main conference is made up of the accepted talks which become orals, posters, and spotlights. Each conference is different, NeurIPS does not allow orals for everyone, but the other conferences do. Spotlights are not given by every conference either.
The Call for papers Is prepared by the Program Committee; example here. The call for papers goes out early in the year to give authors time to submit. Due dates for papers vary, they are determined by level 5. The papers are submitted through 2 different review platforms; CMT or Open Review. The papers are managed by Sherry Xue. Sherry has written a document outlining the process for CML Instructions (reference the documentation folder).
All the papers are peer reviewed to deem their acceptance; it is a major task which requires a large number of area chairs and reviewers. Ethics guidelines are now a part of the paper reviews, see the guidelines here. This part of the conference is time complex and time consuming, Level 5 waits for the results to plan next steps.
The schedule is decided by the General Chair and program committee. At a physical conference, the General Chair will need to know the rooms we have reserved in the venue in order to work on the schedule. That will dictate how many parallel sessions we can manage. Virtually, the schedule will be based on time zones.