"What would you do if you want to have a 1pm lunch?"
Hmm... with such a small roast, that is a bit tricky. Way I see it, it depends on when you want to lose sleep - at night or in the morning.
If at night, I'd get the coals ready to go and throw it on at 12 or 12:30. Helps if you have a remote therm with an alarm, I'd wait to get the temps stabilized, then go to bed around 1 or 1:30. Plan on it being done anywhere between 5 a.m and 8 a.m. (I find smaller butts take me longer per pound than larger ones... I once had a 4 pounder take 13 hours). Then, wrap it a few times in HD foil and hold it. [many options here. If it comes off at 8 or 9, put it in a preheated cooler (a small one that just fits it, or use hot towels from the dryer to fill the extra space) and leave it in the sun until you are ready to pull. If it comes off earlier - like 5-6, with such a small amount of meat, it won't keep it's temp in a cooler. I would wrap in foil and throw it in a very low oven, if possible (like around 120-140 degrees) or put it back on the WSM and close all vents to snuff out the fire and hold it there. If your WSM is in the sun, it will stay around the perfect temp for a while.]
If you want to lose sleep in the morning, I'd get up at early enough to get it on the WSM at 5. If you find you are starting to cut it close, just wrap it in foil for the last bit and it will quickly push through the plateau and speed the cook.
Good luck.
