Time-aware activities are characterized by a set of timerelated aspects, independently from the involved application domain. For example, an activity may need to reason on facts that are held to be true in specific time intervals, or it may need to be executed at precise time instants. In this paper we present a temporal model capturing these concepts and their relations. The model is described by means of an UML formalization, enriched with OCL constraints where needed. The model turns into a set of architectural abstractions that makes timerelated concepts visible at the application level. This eases the analysis and implementation of time-aware systems and enables adaptivity so that temporal constraints may be dynamically met.