For "ordinary" roast duck, like trad chicken or turkey, you will need 2 ducks for 4 people as they are mostly carcase & fat with little breast meat. Unless you can get hold of a huge Aylesbury! Place the duck(s) on a rack over a roasting tin (deep enough to hold the probably 1-2 tins worth of fat coming out), rub plain flour with salt & pepper over the brast & legs, & press small pieces of butter or fat over the skin. Give it 20 mins @ 200/400/gas mk6, remove & prick (only the skin, not the flesh underneath) all over. Pop back in oven & reduce heat to 165/325/gm 3. After another 20 mins remove & lightly prick all over again. If the breast is turning too dark, put a pice of foil over it. Give it another 20 mins. So, it should take just over an hour. I`d be interested to know the oven setting for that 5 hour duck. I know that some top chefs recommend very long timings at low temps for large beef, say or pork joints. I would guess the duck would be "swimming" in fat in a slow cooker!