Since I don't know what kind of oven I will give you internal temp. after 2 hours 35 minutes start looking for internal temps of 120f. Keep in mind roast should sit and will keep cooking for at least 20 minutes after exit from oven. I cook at 360f.
Pulling the roast out at 120F internal will end up being on the rare side of medium. Or in my opinion burnt to a crisp, but that's just me. You may want to pull it out at 130 and have it coast up to 135 - 140 for medium - medium well. You certainly don't want it to get too dry and tough through overcooking.
Do you have a sauce or gravy in mnd to go with it? Yorkshire puddings?
I don't know if this too late to help the OP. Since it's early Christmas morning here please forgive the cut and paste response from another forum that I made in the past. I hope it might help the OP. If you have a polder thermometer I find them very helpful at home.
Pre-heat ovens to 450. Cook ribs with chuck ends facing fans (home ovens may not be large enough to load in this manner) for 40-60 minutes or until internal temp of 55-60 degrees. Cook time varies by meat temp to begin with (IE how cold is meat from being in the cooler).
I cook the ribs in 2" SS hotel pans, heavier ribs on top, 1 per rack four per oven.
Typically ribs are then transferred to an alto sham or slow cooked. At home you can accomplish this by proping your oven door open with a wooden spoon or using a low temperature option if your oven has one, (dehydrate). Again heavier ribs stay on top if you oven is large enough. Cook at 225 for 1 hour or until internal temp is 110 (rare). On larger bone in ribs you will need a higher temp IE 18# bone in rib 115 = rare.
I hold the ribs for 4-5 hours at 140 degrees before I feel they set up enough to cut. At home you can accomplish this by wrapping the roast in aluminum foil and putting it in a cooler for 3-4 hours. Most coolers will hold the meat above 140 for that time.
Make sure the cooler lid stays tight, they like to pop open from the heat so you may want to place some weight on the lid.
While the internal temperature will continue to climb as the roast sets up it will still finish R-MR. I want an internal temp at the end of 135-140. If I have under age ribs I hold an additional two hours. While it's late for the OP I always let cryovaced sub-primals like this age a minimum of two weeks in the cooler and I prefer 4-6.