To me sleeping through means about 6.30 pm all the way through to at least 5.00 am. This is what Cooper does. I've read the 5 hour thing too but I think that's just silly! I think it's from when they go to sleep at bed time until a decent hour of the morning.

He first did it at 9 weeks but didn't do it continuously until 4.5 months old. But he's had periods where it's all gone out the window (a big one from about 6-8 months). He's back to "normal" for now!