The “after the first egg is laid” rule is for both reasons,the HOSP might get used to the spooker but mostly the bluebird might be scared away if the spooker is up earlier. The egg bonds her to that box.
You can successfully experience watching bluebird babies grow with HOSP around but sooner or later you’ll find you have to trap. It could be right away that you run into HOSP wars or it could be 3 years down the road…But it will happen.
Tammy