I have a pork shoulder cooking in the oven right now at 100° C (212° F). I was planning on roasting it for 7 hours, will this be long enough to cook it safely?  I saw the FDA chart about minimum internal temperatures - but am not sure how to translate that to oven temperature/time. 
100°C for 7 hours sounds just about perfect. The meat will be meltingly tender by then. In fact I think you could go even lower on the temperature if you like, say 80°C or 90°C. Of course, if you want to be absolutely sure, check with the thermometer, but unless you know that your oven is unreliable or you happen to be in possession of the largest pig shoulder in the world I am 100% sure it will be more than done in 7 hours on 100°C. Good luck! 