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Time synchronization plays an important role in wireless sensor networks, enabling correlation of diverse measurements from distributed sensor nodes, shared channel communication, and energy conservation. When designing time synchronization algorithms for wireless sensor networks, a number of parameters needs to be carefully considered, including precision, processing time overheads, memory requirements, and energy costs. In this paper we describe an implementation of time synchronization on a wireless sensor network custom designed for traffic monitoring applications. Each node consists of a magnetic sensor, a microcontroller, and a low-power Nordic nRF24L01+ radio chip. We describe various aspects of our time synchronization implementation, including hardware interfacing, low-level event time-stamping, time synchronization mechanism, and software implementation. We discuss the results of our experimental study focusing on precision and performance overhead.