This topic of contention varies from table to table; some insist that a one-shot that can’t be finished in the designated time is no longer considered a one-shot. In my personal opinion, it’s really in the intention, content, and context of the narrative. If the session was interrupted or cut short and required a second session to wrap things up, I would still consider it a one-shot. If the narration or player choice took too long and required another session, that would still be a one-shot for me as well. When it is clear that the DM placed too many encounters or executed an open ending poorly, I would consider it not a “one-shot” anymore, especially if it spans more than the two sessions’ worth of game time.