By default, all clocks on time-aware controllers are set by the network time. In the absence of PTP synchronization, the network time will be an arbitrary time. Because the Linux OS time is also set by network time, attempting to directly set or synchronize Linux OS time conflicts with the processes maintaining synchronization with network time.
NI-Sync 20.1 allows you to sever the link between network time and Linux OS time and set the Linux OS time arbitrarily. Since Linux OS time is used for timestamping measurements, you can now arbitrarily set the time you want to use to timestamp measurements.