One of the most challenging problems in wireless sensor networks (WSNs) research is energy management. We propose two concepts aiming at saving power in low duty cycle applications. We first suggest a methodology for using hardware timers effectively. Then, we provide a way to calculate microcontroller (µC) configurations with various clock frequency setpoints, while respecting several types of constraints imposed on these frequencies, e.g., by other components of the µC, by protocol specifications, by external factors. Our evaluation shows that this approach can respect constraints while saving as much as 11.12% of energy when compared to a popular WSN operating system (OS).