в следующую субботу

next Saturday

→ в
phrase Rare #41,237
next Saturday Used to refer to the Saturday immediately following the current week or the upcoming Saturday. The adjective следующую agrees with субботу in the accusative feminine case after в when indicating a specific time.
RU: Мы встретимся в следующую субботу.
EN: We'll meet next Saturday.

В следующую субботу ее отпустят.

She will be released next Saturday.

— Мой сосед Тоторо (1988)