This is a problem you’ll never solve. Your friend should change the admissions criteria.
As another commenter suggested, if I truly wanted to prevent anyone from abusing the system, I’d take all submissions within the first N minutes and pick a random entry from that entire sample. Instead of trying to solve the original problem, prevent it entirely.
As another commenter suggested, if I truly wanted to prevent anyone from abusing the system, I’d take all submissions within the first N minutes and pick a random entry from that entire sample. Instead of trying to solve the original problem, prevent it entirely.