Context-Oriented Programming (COP) is an approach to improve modularity of context-dependent behaviors. Most COP languages modularize context-dependent behaviors using layers, which are rarely instantiated explicitly. Using the existing layer mechanism, it is difficult to express a context like “a situation where several objects are selected in a GUI window.” To tackle this problem, we propose a new type of layers, which we call temporal layers. A temporal layer is different from existing layers in that it is used by creating its instance, and the extent of its activation is its lifetime. The scope of its activation can be defined by declaratively specifying the exclusion condition in the layer’s enclosing partial classes. This scope can be dynamically and reactively changing. Using a temporal layer, we show a case study of contextual timetraveling, which demonstrates the effectiveness of our proposal.