Aware of this term but I never use it. It is a bad term because it evokes the notion that trading during the first hour of day has less competition. Obviously, there's a large number of specialized professionals/entities that trade the opening hour precisely because there are comparatively big mispricings to take advantage of. Also, first few minutes are rather different from the rest of the day altogether so "amateur hour" is an over-simplification that is probably just damaging.