I guess you want to prevent inserting appointment on last Tuesday of month. If so one suggestion would be attaching the 'OnClientAppointmentInserting' event cancel the event based on condition.
JavaScript:
<script type="text/javascript">
function OnClientAppointmentInserting(sender, args) {
var dt = new Date();
dt = args.get_startTime();
var weekNum = dt.getDay();
// Now Check for whether the date is last tuesday of month