I cook faster and have done enough that I have a basic time frame for several temps. But, I like to leave a 3 hour buffer from end of cook to service. If I am cooking on a schedule, I go for 280F to 290F, I allow 45 minutes per pound. I try to get similar size and shape packers in the 14 to 16 pound range untrimmed raw. I also allow one hour on the front end for coming to temperature from a 225F start temperature. Sets that all important smoke ring that does not matter at all.
So, say I have 12 pound packers, after trimming, I am looking at 9 hours, plus the 1 hour bump and 3 hour rest, I am looking at 13 hours from first fire. If I want to serve at 5, I will start the pit, in theory at 4am.
Reality, I start the pit pretty reliably at 8am. So I run at 300F to 315F and still get it done.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"perhaps...but then again...maybe not..."