head seat (shuso 首座)

Literally "first," "chief," or "head" (shu 首) "seat" (za, so 座): the seat in a sangha hall (sōdō 僧堂) held by the monk deemed leader of the sangha hall assembly (sōdōshu 僧堂衆), also called the great assembly (daishu 大衆).

This was an abbreviated retreat. Abbreviated retreat (ryaku kessei 略結制)  are  offered and practiced  in Japan.   Abbreviated retreats in Japan, may last only a few days.