How can I get the exactly measure time of 3dm gx5 AHRS.

[sinopec]

I cant use a GNSS receiver as time source (because of the enviroment) ,how can I keep time synconized between the device and my pc.
Or How can I get the exact latency betewwn the colloect time and the IMU measure time, .after I get the collect timestamp from the packet infomation,throuhg MSCL.