Well, I tried again at lunch to see if I could spot Comet McNaughton during the day, just in case it was still bright enough. No luck, but I set my camera on max zoom and took a set of pictures in roughly the right area, just to see if I could spot something.
And, well, I did. I’m just not sure what. This was 1:28 pm (33.66 N, 117.75 W), looking roughly southwest, with the sun placed behind a wall to the right. The sun is to the right and above the frame. I don’t have a good sense of distance in the sky, but this is in the right direction to be either Venus or the comet.
Or it could be a passing high-altitude airplane that I didn’t notice.
If it is the comet, the tail is completely invisible, as it should be stretching down to the lower left (away from the sun) and I can’t make anything like that appear with any of the image enhancement tools I’ve tried.
This is unprocessed. All I did was load it from the camera and crop it. And here’s a copy of the whole photo (this was at full ~3x zoom on a Canon PowerShot SD600) with the position of the object and the rough position of the sun pointed out.