A depression in my nest box's bedding material has suggested for several days that a female screech owl is planning on nesting there. Last night, I finally saw one of her visits, when (sure enough) her primary concern was moving the bedding material around to create a depression for the eggs that are on their way. This is normal pre-nesting behavior for a female screech owl, so it's a very good sign that my Owl Cam' will return this year.
Therefore, yesterday afternoon I brought the box down and gave it a thorough cleaning, and a new floor covering beneath the usual bedding material. The new floor covering is composed of unjoined, loose fitting segments of wood that are positioned end-grain-up. It should provide better thermal insulation (more like a cavity in a tree), while wicking away moisture in the bedding material (again, like a cavity in a tree, where the dead, interior wood of the tree is potentially a large moisture sink), providing a barrier to insects like last year's ants, and allowing the box to drain if a meaningful quantity of rain should ever find its way into the box (which has never happened). The latter two requirements border on being contradictory: providing good drainage means allowing unobstructed access to the large drain holes in the box's floor while keeping insects out means, in part, obstructing access to those holes. Realistically, it probably won't be perfect at either, but I think it'll be an improvement over my previous approaches to the problem.
Last night I observed both the male and the female in the box at various times. The male arrived first, examined the cleaned-up interior briefly, then climbed into the entry hole and called for his mate with great vigor. After 5-10 minutes of that, he left. Perhaps his mate had arrived in the area, or maybe he needed a stiff drink after all that calling. Several hours later, his mate appeared in the box, gave it a careful looking-over from the safety of the entryway, and then entered and proceeded to give the bedding material a thorough kicking about, until she had created a shallow depression that met her specifications.
In my experience, that behavior means that nesting could begin at any time.