For most of my schools I will be applying early action, so the decision dates say, “BY december ??” I want to know how often schools release decisions before the deadline.
This isn’t a very useful question unless we know the school you are talking about. Different schools have different admission deadlines and most won’t apply to your situation.
Read each school’s admissions website, it generally gives a timeline.
However, for most schools where the EA deadline is about November 1st, the decisions come out around early or mid December. Most notifications, I believe, come out December 15.