3-4 hours I'd imagine.
It will vary. What were the battery specs when you bought the machine new?
Do you have Bluetooth and wifi on? What about screen brightness and running apps? It'll vary ... that's about the best anyone can say.
Those specs are very promising seeing as I only get like 40 mins tops as I said. I didn't buy it new, I actually bought second hand about nearly 2 months ago, maybe its just not an official apple battery?