Whole Brisket & Boston Butt on UDS Question

I normally use one rack for a butt and brisket, if they fit easily, with air flow around them both. If there is any crowding, then brisket on bottom, butt on top.

Timing is really about temperature, if you are really shooting for an 11, I assume you mean 11pm, then 275F will get you done too soon. If you are talking 11am, then you are not going to make it. As I see it, at 300F, you are looking at 5 hours cook, 2 hours rest, 7 hours total, in best case, your timing works. At 275F, you are going to be eating at 9pm.

Oh yea definitely on one rack, they'll fit easily.

Never done both at the same time. Doing just a brisket you would have no problem with that timeline.