Looking for diurnal or sidereal effects in a GPSDO...

You won't see it on a normal ADEV/MDEV plot:

There is the slightly hint in a "many tau" ADEV plot:

Zoom in to see it more closely:

Even more zoom tells us it's between 80,000 and 90,000 seconds:

Knowing that a sidereal day is 86164 seconds and a solar day is 86400 seconds, we can compute ADEV for each and every tau from 86,000 to 87,000 and locate the dip. Doing this and zooming to the extreme, we see minimum ADEV occurs at about 86157 seconds:

The value is not constant. It varies SV to SV. It varies year to year.

Note the scale on the left is very, very small. Measuring this takes good equipment. For this GPSDO, the ADEV (tau ~1 day) is about 4.7e-14. And the grid lines are 1e-18. For more information google: GPS orbit repeat times