Abstract: “Event-B is a formal language for systems modelling, based on set theory and predicate logic. It has the advantage of mechanized proof, and it is possible to model a system in several levels of abstraction by using refinement.Discrete timing properties are important in many critical systems. How-ever, modelling of timing properties is not directly supported in Event-B. In this paper we identify three main categories of discrete timing properties for trigger-response patterns,deadline,delay and expiry. We introduce language constructs for each of these timing properties that augment the Event-B language. We describe how these constructs have been given a semantic in terms of the standard Event-B constructs. To ease the process of using timing properties in a refinement-based development, we introduce patterns for refining the timing constructs that allow timing properties on abstract models to bere placed by timing properties on refined models. The language constructs and refinement patterns are illustrated through some generic examples.