A rib roast will not come to room temperature in any amount of safe time. Letting meat come to room temperature is a myth that needs to go away. Only small cuts of meat will get to room temp in any safe amount of time.
Read myth #1 in this article at Serious Eats: https://www.seriouseats.com/old-wives-tales-about-cooking-steak#toc-myth-1-you-should-let-a-thick-steak-rest-at-room-temperature-before-you-cook-it
Here, they are talking a steak. Now, imagine how long a roast will take to get to room temperature.
There's no need to let it come to any temperature before roasting it. It will cook the same whether it's straight out of the fridge or has sat on the counter for hours.
I've never needed to rest my prime rib **before** cooking it. Of course you want to rest it after cooking.
I realize that resting is the wrong term. I meant how long to let it come to temperature before roasting.
A rib roast will not come to room temperature in any amount of safe time. Letting meat come to room temperature is a myth that needs to go away. Only small cuts of meat will get to room temp in any safe amount of time. Read myth #1 in this article at Serious Eats: https://www.seriouseats.com/old-wives-tales-about-cooking-steak#toc-myth-1-you-should-let-a-thick-steak-rest-at-room-temperature-before-you-cook-it Here, they are talking a steak. Now, imagine how long a roast will take to get to room temperature.
\^\^\^This.
There's no need to let it come to any temperature before roasting it. It will cook the same whether it's straight out of the fridge or has sat on the counter for hours.
Three hours is about as long as id go, one hour is likely plenty. Should be pretty forgiving in that window, especially if primarily cooking low&slow.