Well you cook it till it hits 135 in the middle..however long that takes.
Would talke a wild *ss guess of around 4 hrs. depending how cold is the meat and if the heat remains constant. Unless you got CAB or at least Choice Grade Sirloin you might should be thinking of somebody with a commercial grade slicer who can cut it thin enough to be edible. If the meat be tough..it hard to cut it thin enough to be chewable with a knife. The typical Select grade sirloin we get around here a person be fortunant to be able to stick a fork in the gravy.