About half past three, I find!
Actually, I think it depends on how much feedback you want and how quickly. As you say, it is different for short stories and poems. I would be more inclined, had I a spare moment or two, to read a short story or poem and comment on it, rather than start wading into chapters of novels. Novels seem to require more commitment somehow. With the two day posting rule in place anyway, I would say post and be damned (or hopefully not) whenever you feel a piece is ready.
Sue