In the last few years, there has been an increasing interest in the Web service composition problem. In the literature, the proposed frameworks investigate mechanisms for synthesizing a composition based on operations and/or messages choreography constraints. The messages choreography constraints depend not only on messages, but also on timed properties. Specifically, we mean by timed properties the time window within which a message can be exchanged. In this paper, we present a formal composition approach to cope with timed properties of asynchronous Web services. We present how modeling the behavior of Web services augmented with timed properties. Then we present a mechanism to deal with such properties when building a composition.