Time synchronization is the most fundamental service to many wireless sensor network applications, which count mainly with low-power devices. This paper focuses in proposing and implementing a time synchronization service for low-power wireless sensor networks using low frequency real-time clocks in each node. This work present the design, implementation and test of an adaptive algorithm, making the timing of the clocks convert as quickly as possible and after this conversion, keeping them most similar as possible. The goal is to achieve the best method that ensures right timing and still having low energy consumption. Experimental results provide evidence of the success in meeting this goal.