What happens if a student arrives for a final after the proctors close check-in?

I’m curious about what happens if a student arrives for a law school final after the proctors close check-in, but not technically after the exam has started. My school requires us to arrive at least 15 minutes early, and once that window closes, proctors stop checking in. So if someone shows up one minute past that cutoff, they’re sent to the academic services office. I’m wondering how the school handles situations like that and what happens to those students. It’s not in the student handbook.