Would cooking a leg of lamb for 12 hours be a problem? I found a nice recipe for a leg of lamb. It is however supposed to be baked for four hours.

It would be more practical for me if I could let it bake for 12 hours (overnight) -- would 12 hours vs. 4 hours be a problem? 

I was planning to seal the pot and set the oven to 110°C (230°F)

EDIT: did it. 2 hours at 180C then 12 hours at 90C. The it was sealed with plastic foil (heat resistant) It was fantastic.
It shouldn't be a problem. I would probably use a lower cooking temperature however. Start with a highish temperature of about 180-200C, to bring the meat out of the danger zone quickly, then lower it to 80-90 for a long slow cook. You will probably want to introduce some liquid to the pan to avoid it all drying out.