I hate to sound like I'm defending, but it's hard to imagine what exactly happened. We're probably dealing with a very complex network with a lot of servers involved. I could imagine that at some point, some technician probably noticed things being off, parts of data that is corrupt or changed in some way alluding to perhaps a malfunction. Then a cup of coffee later, at some point after a little bit of digging, something seems terribly wrong. Now how fast do you think this kind of information passes up the ranks? How fast do you think you know of the true extend of that your system has been intruded and how much is at stake? Then after you know, you start to evaluate. Maybe the person in charge at the time isn't present, so it takes another few hours to get the message through "housten we have a problem". This isn't the type of company where you have a couple of technicians and a boss who is readily available to react to everything immediately.
You just don't shut things down, not when you're network has millions of customers accessing data at all times. And sending out 77 million email again is no small feat. I don't believe for a second that the true extend of the breach was something that was known quickly.
Unfortunately, I don't think anyone will ever know the true extend of how the system was breached and how long it took Sony to figure that out. Of course it's somewhat disappointing for the network to go offline and for it to take them so long to make some notice about what happened. Then again, I'm not really sure I even trust the official statement that they turned off PSN or that when they did, they knew exactly what they were dealing with. That might explain their "back-foot" reaction since they've been offline and why we are hearing about what has happend so late.