I have 17lb (!) standing rib roast (bone in, cradle cut), how much time do I allow for it to come to room temperature before roasting??

No answer here, but I'm just curious: what is a cradle cut? Is that the same as frenching?

Agree with Chops.
No time.
See J Kenji Lopez-Alt comment 10 Jan 2013 in his article on cooking rib roast - he says bringing to room temp takes a long time and accomplishes nothing.
http://www.seriouseats.com/2009/12/the-food-lab-how-to-cook-roast-a-perfect-prime-rib.html

If it was my roast I wouldn't worry abut bringing to room temperature from the refrigerator, unlike other cuts of meat.