When does the blood clot falling out after wisdom tooth surgery usually happen?

Clot: Typically clots don't fall out but are a matrix for tissue to form over the clot and heal the socket.

Ideally you: Don't want the blood clot to fall out. The blood clot is the foundation matrix for the formation of bone to fill the socket. If the blood clot is to degenerate / be lost then you develop a dry socket (48-72 hours) post extraction. If you adequately follow all the instructions given post extraction hopefully you should be fine. Hope this helps.