A method and apparatus for scheduling appointments in a manufacturing process flow are disclosed. The method and apparatus include a number of aspects including appointments in which processing windows float within commitment windows; appointments in which the processing windows include consumption and processing intervals and in which the processing windows can overlap with the processing interval of other appointments; the use of different kinds of calendars including different types of appointments maintained in a variety of states; a calendaring system in which appointments are constrained by the implicit constraints not represented by booked appointments as well as the explicit constraints represented by booked appointments; calendar manipulation techniques used in managing the calendars; and corresponding appointments maintained over multiple calendars in a synchronized manner.