The paper discusses the influence of the time synchronization technique on the synchrophasor estimation accuracy in modern Phasor Measurement Units (PMU). Specifically, we make reference to Global Positioning System (GPS), Precision Time Protocol (PTP) and White Rabbit time disseminations. The paper presents a PMU integrating the three technologies, and assess its performance in steady state conditions. The experimental validation demonstrates that the more deterministic the time source, the better the performance in terms of phase estimation accuracy.