Some recipes say to blast it at high heat for 15-20 minutes, then reduce the heat to low and let it cook slowly, but then I saw a recipe which says it only takes 1-2 hours to cook? Any advice?
Myself I would skip the "heat blast". I would spread it out on a board and then make some diagonal slashes in the skin. You can stuff it with practically anything: sausage, artichokes, olives etc, then you will need to tie it up and roast it to about 145F. Now it's done. Let it rest.
I'm with you, however, keep in mind that this doesn't have the skin on it. It's simply deboned, and butterflied. So that's why I was curious on how I should approach cooking it. High heat blast to brown the outside, then reduce the heat to let it reach temp gently until 145F.
I've become a fan of the reverse sear method. Cook it low and slow until you're about 10 deg under your temp. Then warp 10 to sear the juices inside. A rub with olive oil will really brown up nicely. The theory is that searing at the end will allow for a more even cook in the beginning and then sear the juices in at the end. Give it a try if you're feeling frisky.