Ages. It'll depend on the size of the cavity, the mass of the meat. Could take 5 hours plus. However, bringing meat to room temperature isn't necessary. Really, it doesn't shave anything off the cook time.

As per usual, Serious Eats did some investigation into allowing meat to come to room temperature. Steak in this case, but the principle stands.

http://www.seriouseats.com/2013/06/the-food-lab-7-old-wives-tales-about-cooking-steak.html

It doesn't necessarily have to come exactly to room temp, but I always let my turkey sit out for one hour.