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As I understand the rules, the message means that in 24 hours the system will check for answers which satisfy the conditions described in https://mathoverflow.net/help/bounty, and if it finds one which does, it will auto-award half the bounty amount to that answer. In your case this means that unless someone adds another answer within the grace period which gets at least two upvotes before the grace period ends, nobody will get the bounty -- the referred help page says "If there's no answer meeting those criteria, the bounty is not awarded to anyone.".