It seems unlikely that any pro, handed 5 bats or whatever for free, would have the time or the inclination to knock them all in. So - in my opinion - it's safe to assume that they 'ping from the get-go'. For the rest of us, the main questions are how much time do I have spare for knocking in, and how long do I want a bat to last for? For me personally, I have no time for knocking in, never have. I am happy to get a new bat settled in nets, with used balls. Seems to work OK. But then, I'm not at all concerned about dents and cracks on the face and edges, for me these are badges of honour. I like my bat to look worn, I like marks, I like adding a bit of tape. I like a bat that I can study after a long inning and remember how certain marks were made. I also strongly believe that a worn, cracked bat is better for taking the shine off the ball, which is my job after all.
The only exception I make at first is the toe. I do knock the toe in for a few minutes, hitting hard with a mallet. Digging out pacey, new ball yorkers is a bat breaker, so worth trying to guard against. But you know, stuff happens, and if I need to buy or make a new bat each year, that's fine with me.