I'm watching Dateline right now about a different case and the narrator says that the young man tried to file a missing persons report but the Miami Police wouldn't let him until she had been missing 24 hours. Is it different in different jurisdictions? Was the Miami Police Department just lying? Was the show in error? This is why people believe you have to wait 24 hours!
It can. However, when small children are missing...I think those rules are not applied. MOST people would immediately seek professional help to find missing children. So will most jurisdictions.