Sorry Bionic, I didn't reply about the timing for a joint. I'm not totally sure of exact times, as that's not how I cook.
You would weigh your leg and cook it in a conventional oven until it was fully hot - it won't be cooked right through. Then transfer it, in it's covered pot as clodhopper points out, to the hay box. I tend to cover the lid with a tea towel or similar to prevent hay dust getting inside. The time in the hay box really depends on how long you want to leave it. It could be just an hour as you take it somewhere, or pop down to the shops, or it could be all day. It won't burn, just become amazingly tender while staying moist. When you then come towards dinner time, check it's done, then crisp it in the oven for half an hour or so.
So there's nothing exact about it, just what suits you. I suppose that for the turkey, it's almost completely cooked before I put it in the hay box, but that's mainly for transport.
Stews and casseroles are a bit different as you are using the haybox more as a slow cooker.
Just give it a go - if it's not fully done, just leave it in the oven afterwards for longer.
Clodopper, your army hayboxes sound very state of the art
as one would expect.