Generally you wrap around the time of the stall or when the meat has developed enough bark. For a brisket, this tends to be in the ~170° range.
Humidity is a major factor in shortening the stall, because the stall comes from evaporative cooling as the meat loses moisture. If you keep a large water pan at the hottest spot of your cooker, this makes the stall dramatically shorter because there will be less evaporation in a humid chamber.
I will reiterate that for a brisket, the flavor you’ll get from wrapping in butcher paper is far superior to that of a foil wrap. I live in Austin and have tried all of the best brisket around here. Anything wrapped in foil (i.e. Snow’s) is in a tier far below the best places (Franklin, La Barbecue, Micklethwait), every one of which wraps in butcher paper. There’s a reason for that! The aluminum foil really does inflict a distinctive pot roast flavor from the steaming of the brisket, a flavor that does not occur with butcher paper wrapping.
Beyond that, the other most important advice (noted elsewhere in this thread) is to allow a very long rest period after the cook, ideally 12+ hours at around 140-145°. This is what causes the brisket to really relax and the rest of its collagen to melt without drying out. My brisket cooks these days use a schedule similar to Franklin: cook all day, aim to finish just before bedtime, and then rest in a low warmer all night for lunchtime bbq the next day.
Pork butts are a very different beast and none of the above advice is applicable there, except the importance of a water pan.