Once we find extraterrestrial intelligence, how long will it take us to communicate with it?

It seems too cruel to believe we're the only technologically advanced species in the cosmos. We couldn't possibly be the only ones, with so many stars and so many habitable planets out there.

So we're all waiting eagerly for the discovery of incontrovertible proof that aliens are out there, mining their asteroids, building cities or beaming messages into space.

Top image: City in the Clouds by Gate to Nowhere on DeviantArt.

The question is: Once we find the aliens, how long will it take for us to establish actual communication with them? Vote below, and explain your answer in the comments.