Missed Base Appeals

Hi all,Situation: No runners on base. Batter hits a Home Run over the fence, and misses second base as he/she is rounding the bases.At what point is the earliest the defensive team can appeal the missed bag?a) As soon as the Batter-runner misses 2nd base b) As soon as the BR crosses 3rd base c) As soon as the BR crosses home plate d) As soon as the BR enters the team's dugout or other out-of-play areaThanks!