Scrod, the thing you're missing is that the HIG are guidelines, not rules, and aren't always appropriate. In this case, I would think that an "Open at Login" app like Hazel is an exception — you never really "look it in the face" and so for it to pop up an update notification at any time, including login, it is likely to feel like an interruption. Notifying on idle avoids that. I think it's a good compromise, and a nice patch.