On-demand broadcast has been supported in the Internet to enhance system scalability. Unfortunately, most of existing on-demand scheduling algorithms did not consider the time constraints associated with web requests. This paper proposes a novel scheduling algorithm, called Slack Inverse Number of requests (SIN), that takes into account the urgency and productivity of serving pending requests. Trace-driven experiments demonstrate that SIN significantly outperforms existing algorithms over a wide range of workloads. Categories and Subject Descriptors C.2.0 [Computer Systems Organization]: Computer-Communication Networks--general General Terms Algorithms, Performance Keywords Scheduling algorithms, on-demand broadcast, Web, time constraints