I think I'm on to something, at least as far as identifying where the gap originates from. When I was testing this with recent alerts, there was almost always a consistent time gap. But... if I try this with a much older alert, or if I try this from any clip that is not the most recent, the time matches exactly. If I copy the image address on the most recent clip or a number of recent alerts, the time almost always does not match.
I'm seeing a pretty clear divide here. If I copy image address on the most recent clip, the time is off, but that clip is still being "written" to by
Blue Iris. Clip #2 and any older clips are fine and the times match. Of course with alerts it's difficult to know offhand which exact clip that alert resides on, BUT much older alerts that are certainly on an older clip that would have been definitely "completed" or closed from recording with Blue Iris, the time matches then.
So I'm thinking the line in the sand is whether the clip_of_origin is still being written to by Blue Iris or not. If it is, times are wonky. If it's done and Blue Iris continued onward with a new clip, the times seem to match fine.
Not sure how fix-able or needed this is, but since I raised the question I wanted to share what I'm seeing.