I have observed both the male and female owls visiting the nest box on the last two nights, so things are looking good. The male has yet to coax his mate to actually enter the box, from what I've seen. However, his calling from inside the box has persuaded her to stick her head in for a look on a number of occasions. For some reason this has been the pattern every year that I can recall. I don't know if it happens because there are different females each year (in which case the box might be strange to them), or whether this female reticence is just a standard part of the yearly courtship ritual, even among established pairs.
Anyway, everything is proceeding normally, which is a very good sign.