An increasing number of distributed measurement and control applications requires that network nodes are able to estimate the position and the time measured by other devices on a common spatio-temporal reference frame. Accurate packet timestamping is a necessary condition to achieve this goal. However, in the case of wireless networks, timestamping accuracy is generally quite poor due to the combination of multiple uncertainty sources (e.g., variable signal attenuation and interferences) affecting wireless message propagation. Various communication schemes have been proposed to improve performance. One of the most recent and promising is the Chirp Spread Spectrum (CSS) modulation. In this paper, the timestamping accuracy of CSS signals similar to those defined in the standard IEEE 802.15.4a is analyzed experimentally using two different platforms based on a Software Defined Radio (SDR). Some results confirm that CSS can be successfully employed for accurate time synchronization and ranging.