How long to cook a turkey per pound

Sadly no mater what you do, you are going to come out with non-optimal results. I would go with the oven method over the grill as you need to get the meat up, but you want to do it with out losing all the juice/fat you have already taken all the trouble to convert to gelatin. The grill is going to raise the outside of the meat much quicker that the inside (mostly, you can use your grill as an oven but in this case I don't think it brings anything to the table that you regular oven doesn't).

The best way, and by best, I mean the one with the tastiest results, is going to be put the butt in a 200 to 250 degree oven and let it come up to temp. This method is going to take the longest but will preserve the meat that come off the grill as close as you could.

Or, you can heat just like a roast and let the outside overcook a bit.

or, depending on how you are serving the finished product, you can slice cold and finish in a skillet to heat though... this would be great if you are doing sandwiches or pulled pork.

If you are feeling adventurous, 130 degrees plus smoke is a little on the rare side but it would still be delicious... not for this one as you let is cool on the counter top and fridged it but on the next one, I might just eat it then.

The purpose- as with any cooked meat- is to let the meat firm up so it doesn't release juices when you cut into it.

In the case of a turkey it also helps to let it cool enough to not burn you when you are carving and eating it.

Both of these goals will be met in 30 minutes to an hour.

I don't know why that chef would recommend 3 hours. At that length of time the turkey would start to approach room temperature and would be less appealing to eat as well as start the clock on the danger zone.