Good afternoon Roger,
The "danger zone" is the zone in which most bugs will multiply and cause trouble. The key isn't how long food is above 40F and below 160F while cooking--just as long as it gets to the magic 160F. Same goes for re-heating. The time it takes to get there in either situation is no factor.
Ground beef with its large amount of surface area (from all the mixing of outside stuff with inside stuff is particularly toubleseome. That's why the warnings about rare burgers. Butts,and briskets have comparatively smaller surface areas for their size and don't, as a rule, have deeply imbedded bugs.That's also why you can pretty safely eat your steak rare. Outside bugs are killed by the heat while the inside stays below 160F.
It's how food is treated after cooking that's the deal. For example: properly handled, meat cooked to 160F should be bug-free and ready to serve (hot), cooled in the frig (40F or below) or frozen <32F.) There are some bugs that cause spoilage that are active below 40F but the important ones which cause sickness are not.
That being said, when served, food should be kept below 40F or above 160F according to type of food and specfic guidelines. Also, it should be consumed as soon as possible. The longer food sits out once it has warmed/cooled back into the "danger zone" the greater the chance of re-contamination by other utensils, hands or from the air. The critical exposure time varies with the food.
Long slow smokes to internal temps above 160F are fine and are considered safe. Most cold-smoked foods in which temps don't reach 160F, require additional cooking or other forms of preservation.
Hope that's more help than confusion.
Hook