Please keep in mind, that those are not very precise. High-resolution timer measurements cannot be done in a precise fashion on most windows systems for ethernet applications. You would need to take the time immediately in the MAC receiving the packet, everything above is already adding delays in the time measurement. For exact that reason, most equipment for error analysis in Industrial Ethernet systems (which rely heavily on precise nano- and microsecond timestamps) use external (FPGA-based) hardware to create the trace and 3rd party utilities to provide them to Wireshark.
In other words, microseconds is as reliable as it gets.