Desiato
Hard-core CEG'er
lol, you haven't had one go on you yet have ya? I would say you don't need to change it right at the interval it is recommended to change, but I still would say it is less a pain to change it before it goes. Especially if you don't have another reliable ways of getting around or don't have a couple hundred dollars laying around if you have to get someone else to replace it for you.
I don't think there is a maintenance interval for the duratec timing chain... and if it goes while the engine is operating, it's 3L time I believe.