To guarantee end-to-end quality of service (QoS) delivery of rich multimedia consuming large bandwidth over IP, network resources have to be reserved in advance. To reserve the resources, advance reservation requests specifiy their desired service duration while conventional requests referred as immediate reservations do not. When these two types of requests are mixed, we need to balance them and provide an efficient resource sharing scheme. Focusing that the service time durations are partly flexible and may be adjusted with negotiation (although depending on the type of requests), we propose a new bandwidth scheduling scheme in this paper. The adopted models for service duration flexibility, user utility, and network cost are utilized to trade off the conflicting interests of provider and users and to balance the resource provisioning to both types of requests. By modeling the operation of resource manage (i.e., bandwidth broker) over the differentiated service (DiffServ) QoS provisioning, network simulation is conducted. The performance of proposed scheduling is then evaluated in terms of overall bandwidth utilization, total accomplished user utility, and reservation blocking rate.