The standard advice, for a new play, is that it's smart and helpful for the playwright to attend rehearsals. But the playwright has to be careful to let the director be the one who directs. We're trying to put together a racehorse here, not Dr. Doolittle's 2-headed pushmi-pullyu:
I don't mind hearing what the actors or directors have to say about the play or the characters. But being sensitive people, they often worry about offending me. I think it takes them a little while to get used to me being there.
They usually find some things about their characters puzzling - things I may not have found puzzling at all. I may even think, in the moment, that I have an answer for them. But a lot of the actor's art is actually taking place at precisely this step - where the actor tries to get a grip on the character.
While they develop their grip
I mostly zip my lip.