Hugh, I don’t know how many years I have been using wren guards on boxes. Some females take longer than others to adjust; some males never do. Ultimately, all females will figure out a way to enter the box if there are eggs inside.
Yes, the ideal time to install a guard is within a few hours of the first egg. That gives her the rest of that day to figure things out. However, with wrens around you can’t be too careful and I would still try to help her make the adjustment.
This is 3 days later. Did she deal with the gradual lowering of the guard?
Gin
Atlanta, GA