I have smoked butts at 225F, 350F, and everything in between, including starting at 225F and finishing at 350F. When we had pot lucks at work, I'd smoke them overnight at 300+F then take them to work in the morning, reheating later in crock pots. Trust me, butts don't care what the temperature is of your smoker or oven. It is the most forgiving piece of meat on the planet.
Choose any temp you like and smoke away. 275F is absolutely fine. When it is probe tender, it is done. It can rest for hours if need be, but you'll be right on time with a 6 AM start.