In this paper we address the problem of qualitative and quantitative analysis of timing aspects of Web service compositions defined as a set of BPEL4WS processes. We introduce a formalism, called Web Service Timed State Transition Systems (WSTTS), to capture the timed behavior of the composite web services. We also exploit an interval temporal logic to express complex timed assumptions and requirements on the system?s behavior. Building on top of this formalization, we provide techniques and tools for modelchecking BPEL4WS compositions against time-related requirements. We also present a symbolic algorithm that can be used to compute duration bounds of behavioral intervals that satisfy such requirements. We perform a preliminary experimental evaluation of our approach and tools with the help of an e-Government case study.