Multimedia presentations are applicable in various domains such as advertising, commercial presentations or education. Multimedia presentations are described by multimedia documents. The presentation of multimedia documents require vast system resources due to the huge amount of data that has to be transferred and processed by the computer system. If multimedia documents can be accessed on-line via different types of networks and be presented on various types of terminals, such as PCs or Set-Top-Units, different amounts of resources may be available at presentation time. Hence, it can happen that there are not enough resources to render a multimedia document according to the specification. For usual multimedia documents resource scarcity implies an arbitrarily reduced quality of the presentation or it can even be impossible to start or continue the presentation. To handle resource scarcity in a better way, multimedia documents can be specified flexible so that they can be adapted to different resource situations. Our temporal model provides abstractions to specify flexible multimedia documents on two levels. It is possible to specify multimedia documents with alternative presentation parts. Further on, the presentation behavior of media objects can vary within specified limits. Hence, the temporal model allows to compose presentations which have a defined behavior when resource restrictions occur. The presented adaptive scheduling algorithm uses the flexibility in specifications to adapt presentations at regular intervals to the current resource situation. Hence, the quality of presentations is reduced or increased in a defined manner