Joy of Cooking says that we should expect the leg of lamb to take 8 to 9 minutes per pound to cook. Ours was a between 4 and 5 pounds, so we allowed an hour. Pulled it out, let it rest for 10-15 mins, then started to carve. The center was still pretty pink, so I checked the temp and we’d only hit 105 F internal. No bueno.
So now we’ve got it back in the oven for 20 minutes. Meanwhile, everything else is finished. We will rebuild, we will reheat.
Hope your cooking is going better than mine.