Why would human activity impact the probability of LIGO event detection? Is this because LIGO operators are doing certain things to the detector during their work hours, or some other property of the environment around the 2 LIGO detectors?

At first I grumbled mightily because I couldn't see the point to it, but after I'd plumbed everything through, I could definitely see the data points snapping in and out of alignment when turning on and off the DST adjustment.

Assume a "moderate" ~45° slope or sine wave... typical diurnal traffic pattern. When shifting by 1hr, that's either 1/24 or 1/12 (call it 5-10%) of "deferred peak traffic"... definitely detectable even with moderate sensitivity.

DST support gave us back confidence in alerting over an abnormally large time range too! Most alerts were set up with a 10-week lookback, discarding both the highest and lowest weeks, so DST changes twice per year potentially threw off alerting for up to 4 months!

I have no doubt that I could detect DST with damn near anything, let alone some crazy calibrated laser inferometer machine!

that's what you get at the extreme precision installations - you can measure all the people around