2 years ago i did the same thing as you - searched and found the 550 instructions and figured what the heck i would try it... i did my math carefully and about 1 minute before the oven was to be turned off it started to smell - burnt... oh i was mad... after spending so much money on this and it was burning ARGGG... so i continued on let it go for the last minute and turned the oven off... i am proud to say i resisted the urge to peek (that was the hardest part LOL) when the 2 hours were up i pulled it out expecting it to be terrible OMG i was so surprised!!! it was perfect! absolutely perfect! For the first time i cooked prime rib at home and it tasted just like restaurant prime rib!!! I have used this technique several times on prime rib and even regular roast beef and wonderful every single time... I have played a little with the amount of liquid i add... i like au jus... so i add liquid to the pan... give it a try you will not be disappointed mmm i can hardly wait for my new years dinner now :-)