At midnight I decided it was time to go. The plume of the heat plant 6 km from my place had developed a kind of bend that could signify an inversion just starting to set in.
Turned out there was still plenty of time. It was windy and dry at the slopes. The gunning plumes died right away. Nothing else to do but wait.
Clouds arrived, covering more and more of the sky, but they were too high. Finally after 3 o'clock the action started, either because the cloud base lowered or it cleared up. It is not always easy to know because in clear sky conditions snow gunning makes often its own cloud some way above the ground, which may be thick enough to block even the full moon.
I started with a failed attempt to photograph on the incline of the eastern Totto slope where they had not yet made any snow. The swarm left me just as I got the equipment in place. A little later on the golf track I managed to get a handful of photos before the swarm shifted again. But I botched it by taking only the lens cap off my new 4.5 mm Sigma lens, not the lens hood. When I realized the mistake, the display was already declining. In general, the combined lens hood + lens cap of this lens is not that great. The lens hood thread is endless and you spend a life screwing it off.
I called it quits at 6:30 because the display was steadily worsening. As I drove to my place, and out of the diamond dust for first time since the action started, the sky cleared up. So, as to the question posed in the beginning of this post, whether this was a clear sky or punch hole display, the former was true.
In hindsight, I should have done spotlight instead of lunar. Wouldn't have had to worry about the movement of the light source, and even with all the light pollution from the streetlights and moon, it would have most likely been the more interesting option results wise.