In this paper we analyze the influence of the frequency of sensor data readings on the behaviours of a Robotic System (RS). This is done in the framework of behaviour based architectures drawing inspiration from biological and ethological evidences. In the first part of this paper we recall some notions on biological clocks, showing how to represent those clocks in terms of Schema Theory. Then, we propose an architecture in which the frequency of access to the sensory system is modified in accordance with environmental changes. We evaluate the results obtained in experiments with simple behaviour based systems in unknown environments with obstacles. In the last part of the paper, we briefly discuss the possibility of extending the proposed model to more complex robotic systems and to teams of robots.