It doesn't necessarily need to be "carbonated" right away, you just want to make sure and purge the regular air out with CO2. If I know I'm going to let a beer sit for a while, I just purge the oxygen on kegging day, then maybe hit it with some CO2 every couple of days, when I think about it. Really the only thing you need to worry about is getting any oxygen away from the beer.
I usually don't bother worrying about actually carbonating the beer until it goes into the kegerator.
As Rockn said though, if it's an IPA, don't let it sit too long. It's not about spoilage, but losing that upfront hoppiness that you want in an IPA.