If you go with the same temperature as normal, the butt will take longer than you are used to. I have had it go various ways, from brisket first to butt first being done. At 275F or so in a small cooker, like a kettle, it will be 7 to 8 hours, in a UDS, I had one recently that the brisket clocked in at 5 hours, the butts at 8 hours.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."