Spot checks were performed on GPSTIME: 1256605434 to check that timing is correct prior to the start of O3b. The IRIG-B timestamp is in agreement with the timestamps written to frame files within +/- 10 seconds of the given time, and DuoTone delays are within 1 microsecond for ADC channels at LHO. Timing checks at LHO are as expected and consistent with the absolute timestamps. 

Scripts used to run these checks can be found here: https://svn.ligo.caltech.edu/svn/aligocalibration/trunk/Common/Scripts/Timing