There is actually two different foil times. The first is a matter of choice as to when you feel that the meat your smoking has gotten to a point that you have created the amount of bark you are happy with, you have introduced all the smoke flavor you are wanting and I prefer to hit 160 = 170 degrees. If I'm planning to foil, this is when I do it. I've also foiled at 190 to get it done in the oven at a higher temp cause company is comin. At this point you are baking and not smoking so it actually doesn't matter where the heat source is coming from... your already hot smoker or a preheated oven... etc. You are baking. The next time to foil... unless your already foiled up, is when you take your meat off and let it rest. That again is a matter of opinion. I have taken butts out at 190 and I've taken them out at 205. I think it has to do with the cut of meat. I've learned through the forum how great this rest period of time is. I always at least rest my meat in the foil with a couple of towels over it for an hour or so at the minimum. (OK..... I might have pulled off a chunk to taste test.... or two). If I need to I can wrap it in towels and put it in the cooler and still serve it piping hot 4 or 5 hours +. Gives you a lot of room for error.