I cooked mutton shoulder like advised in the answer for this question. It was under the foil and was cooked in the oven for like 3 hours.
Now I have mutton leg instead of shoulder. The size is similar. Should the cooking time be different?
Leg is usually leaner than shoulder and so doesn't benefit from a long slow cook. A quicker, hotter roast is generally best, something on the order of 2-2.5 hours @ 220C for a good-size leg. Let it rest for a good half hour afterwards.