Maybe the question is not so much a matter of when to ask, but whom to ask. I mean, does the father: a) validate the son's complaint?, b) respond to it epathically or sympathetically?, or c) admit the wrong and try to right it, e.g., "Hey, I hear you. Today we celebrate little bro, but tomorrow, it will be all about you."
Maybe, sadly, the dad is not far long enough in his receovery process, as an emotionall abusive parent, to see offer emotinal presence to his son. I mean, does he? he may be working out so much guilt for his faiures as a pop, the ones that the little bro's flight brought to the fore of his consciousness, that he cannot take on another breach or boken relationship. One breach at a time. That dad, I feel for him; he's got to be grieving and doin' a lot of make up for lost time. OR, he may be a changed man.