Nuthatches Still Active in Nest Box

We have been keeping watch on the "big" nest box on the back end of our property where White Breasted Nuthatches took up nest residence in early March. So far, that nest must be an active concern. I have seen a bird making regular visits, and as recently as yesterday. The good news is that I only see one of them, in contrast to the "explorer phase" when two could be seen in proximity to one another. The courier bird (I assume the male) has an interesting behavior: it exits the box, then shimmies up the ash tree where the box is hung for anywhere from three to five feet, then flies off. I can't believe this fools any opponent; after all, I can see this behavior perfectly well. When will the chicks fledge? All the material I have suggests I must wait until May to see if any young make it. And that is the big question: all of my nest boxes have been busts for years. But at least for now we have high hopes.