How many minutes between 115 F and 120 F for a ham? I'm preparing this ham recipe.  It calls for a ham 7 to 8 lbs. Well, I ordered a ham described as "7 to 9 lbs" and what got delivered was a hair under 10 lb, so that's what I'm using.

Using the recipe's 20 minutes per lb instruction, I popped that ham in the oven with the understanding that it would be there for three hours and 20 minutes, total.  The recipe says to glaze the ham with 40 minutes to go, and when the internal temp is 120 and 125 F.  So at 2 hrs and 40 min, I checked the internal temp, and it's 115 F.

How much longer does it need to be in there (325 F) to get up to the 120-125 range?

I have no way to check the internal temp without opening the oven door and pulling out the ham, so when should I do that?  (My natural inclination would be to check like every thirty seconds which I understand is counterproductive.)
Probably another 10-20 minutes. The interior should be heating somewhat faster now than it did initially, since it took a while for the heat to propagate all the way in. And assuming it was refrigerated at 40F, it's averaged about 10F increase every 20 minutes. (Your 15-20 minutes outside the refrigerator isn't going to change that much.)

It's also really not that sensitive, so it doesn't matter that much if you over shoot. So I'd check after 10 or 15 minutes, and if it's not all the way there yet, you'll at least have a good idea how fast it's heating.