Functional reactive programming (FRP in short) abstracts values that change over time as time-varying values and the timing of responses as events. Using these abstractions, reactive systems are described as data flows between time-varying values and the occurrence of events. In this paper, we propose TEFRP, a functional reactive programming language for embedded systems in which the data flow of time-varying values can be switched at each periodic timing. The ability to switch the update method at each time facilitates the description of systems in which the responses change over time. Such systems include, for example, programs that display received data by turning LEDs on and off, and communication protocols that perform fixed pre-processing and post-processing. TEFRP treats the time from the start of execution as an event. Although events in typical FRP are assumed not to occur at the same time, time descriptions may include the same timing. TEFRP allows logical combinations of periodic timings and actively uses such overlaps to improve descriptiveness. This paper also discusses methods of converting logical combinations to simpler forms.